Semiconductor device and method of manufacturing the same

ABSTRACT

To improve the electric performance and reliability of a semiconductor device. A memory gate electrode of a split gate type nonvolatile memory is a metal gate electrode formed from a stacked film of a metal film  6   a  and a silicon film  6   b  over the metal film  6   a . In an upper end part of the metal film  6   a , a metal oxide portion  17  is formed by oxidation of a part of the metal film  6   a . A control gate electrode of the split gate type nonvolatile memory is a metal gate electrode formed from a stacked film of a metal film  4   a  and the silicon film  4   b  over the metal film  4   a.

CROSS-REFERENCE TO RELATED APPLICATION

The disclosure of Japanese Patent Application No. 2011-118722 filed on May 27, 2011 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to a semiconductor device and a method of manufacturing the same, particularly to technology that is effective when applied to a semiconductor device having a nonvolatile memory and a method of manufacturing the same.

As a nonvolatile semiconductor memory device capable of electrical write/erase, EEPROMs (Electrically Erasable and Programmable Read Only Memory) are used widely. These memory devices (memories) represented by flash memories widely used nowadays have an electroconductive floating gate electrode or a trapping insulating film surrounded by an oxide film, under the gate electrode of a MISFET, and utilize an electrical charge accumulation state in the floating gate and the trapping insulating film as storage information to read it as a threshold value of a transistor. The trapping insulating film means an insulating film capable of accumulating electric charges, and includes a silicon nitride film. Injection/release of electric charges to/from such an electric charge accumulation region shifts the threshold value of a MISFET to cause the MISFET to operate as a storage device. As the flash memory, a split gate type cell using a MONOS (Metal-Oxide-Nitride-Oxide-Semiconductor) film exists. This memory has, by using a silicon nitride film as the electric charge accumulation region, an advantage that the reliability of data retention is excellent because electric charges are accumulated discretely. Furthermore, because the reliability of the data retention is excellent, oxide films over and below the silicon nitride film can be thinned to enable low voltage write/erase operation, as compared with an electroconductive floating gate film.

Japanese Patent Laid-Open No. 2010-108976 (Patent Document 1) describes technology related to a split gate type nonvolatile memory, and describes, in paragraphs [0080] to [0082], formation of a gate insulating film GOX from a high-permittivity film.

Japanese Patent Laid-Open No. 2004-266203 (Patent Document 2) describes technology related to a nonvolatile memory element, and describes, in paragraphs [0138] to [0141], formation of a memory gate electrode 36 by an electroconductive film 35 made of a metal and has a resistance lower than a polycrystalline silicon film.

SUMMARY

For conventional split gate type nonvolatile memories, as a stacked gate insulating film, an ONO (Oxide-Nitride-Oxide) film of a stacked structure including a silicon oxide film, a silicon nitride film and a silicon oxide film is formed, and, as a control gate electrode and a memory gate electrode, a polysilicon gate electrode is formed.

Recent years, the nonvolatile memory is desired to have better electric performance and reliability.

The present invention has been made in view of the above circumstances and provides technology capable of improving electric performance of a semiconductor device.

The present invention also provides technology improving the reliability of a semiconductor device.

The present invention also provides technology improving the electric performance of a semiconductor device, and technology improving the reliability of a semiconductor device.

The other purposes and the new feature of the present invention will become clear from the description of the present specification and the accompanying drawings.

The following explains briefly the outline of a typical invention among the inventions disclosed in the present application.

In a semiconductor device according to a typical embodiment, a memory gate electrode of a split gate type nonvolatile memory has a metal film and a silicon film over the metal film, and has a metal oxide portion formed in an upper end part of the metal film.

Further, in a semiconductor device according to a typical embodiment, a metal gate electrode is applied to a control gate electrode of a split gate type nonvolatile memory.

The following explains briefly the effect acquired by the typical invention among the inventions disclosed in the present application.

According to the typical embodiment, the electric performance of the semiconductor device can be improved.

Also, the reliability of the semiconductor device can be improved.

Moreover, the electric performance of the semiconductor device can be improved, and the reliability of the semiconductor device can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of essential parts of a semiconductor device in an embodiment of the present invention.

FIG. 2 is a partially enlarged cross-sectional view of FIG. 1.

FIG. 3 is an equivalent circuit diagram of a memory cell.

FIG. 4 is a cross-sectional view of essential parts showing a modification of a semiconductor device in an embodiment of the present invention.

FIG. 5 is a table showing an application condition of voltage to each site of a selection memory cell in “WRITE,” “ERASE” and “READ.”

FIG. 6 is a process flow chart partially showing process of manufacturing a semiconductor device in an embodiment of the present invention.

FIG. 7 is a process flow chart partially showing process of manufacturing a semiconductor device in an embodiment of the present invention.

FIG. 8 is a cross-sectional view of essential parts in a process of manufacturing a semiconductor device in an embodiment of the present invention.

FIG. 9 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 8.

FIG. 10 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 9.

FIG. 11 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 10.

FIG. 12 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 11.

FIG. 13 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 12.

FIG. 14 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 13.

FIG. 15 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 14.

FIG. 16 is a partially enlarged cross-sectional view of FIG. 15.

FIG. 17 is a partially enlarged cross-sectional view of FIG. 15 in a modification.

FIG. 18 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 15.

FIG. 19 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 18.

FIG. 20 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 19.

FIG. 21 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 20.

FIG. 22 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 21.

FIG. 23 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 22.

FIG. 24 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 23.

FIG. 25 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 24.

FIG. 26 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 25.

FIG. 27 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 26.

FIG. 28 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 27.

FIG. 29 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 28.

FIG. 30 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 29.

FIG. 31 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 30.

FIG. 32 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 31.

FIG. 33 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 32.

FIG. 34 is an explanatory view for explaining a leak current.

FIG. 35 is a cross-sectional view of essential parts of a semiconductor device in another embodiment of the present invention.

FIG. 36 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device in another embodiment of the present invention.

FIG. 37 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 36.

FIG. 38 is a cross-sectional view of essential parts of a semiconductor device in another embodiment of the present invention.

FIG. 39 is a cross-sectional view of essential parts in a process of manufacturing a semiconductor device in another embodiment of the present invention.

FIG. 40 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 39.

FIG. 41 is a cross-sectional view of essential parts of a semiconductor device in another embodiment of the present invention.

FIG. 42 is a cross-sectional view of essential parts in a process of manufacturing a semiconductor device in another embodiment of the present invention.

FIG. 43 is a partially enlarged cross-sectional view of FIG. 42.

FIG. 44 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 42.

FIG. 45 is a partially enlarged cross-sectional view of FIG. 44.

FIG. 46 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 44.

FIG. 47 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 46.

FIG. 48 is a partially enlarged cross-sectional view of FIG. 47.

FIG. 49 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 47.

FIG. 50 is a partially enlarged cross-sectional view of FIG. 49.

FIG. 51 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 49.

FIG. 52 is a partially enlarged cross-sectional view of FIG. 51.

FIG. 53 is a cross-sectional view of essential parts of a semiconductor device in another embodiment of the present invention.

FIG. 54 is a cross-sectional view of essential parts in a process of manufacturing a semiconductor device in another embodiment of the present invention.

FIG. 55 is a cross-sectional view of essential parts in the process of manufacturing a semiconductor device subsequent to FIG. 54.

FIG. 56 is a cross-sectional view of essential parts showing a modification of a semiconductor device in another embodiment of the present invention.

DETAILED DESCRIPTION

The following embodiments will be explained, divided into plural sections or embodiments, if necessary for convenience. Except for the case where it shows clearly in particular, they are not mutually unrelated and one has relationships such as a modification, details, and supplementary explanation of some or entire of another. In the following embodiments, when referring to the number of elements (including the number, a numeric value, an amount, and a range), they may be not restricted to the specific number but may be greater or smaller than the specific number, except for the case where they are clearly specified in particular and where they are clearly restricted to a specific number theoretically. Furthermore, in the following embodiments, an element (including an element step) is not necessarily indispensable, except for the case where it is clearly specified in particular and where it is considered to be clearly indispensable from a theoretical point of view. Similarly, in the following embodiments, when shape or position relationship of an element is referred to, what resembles or is similar to the shape substantially shall be included, except for the case where it is clearly specified in particular and where it is considered to be clearly not right from a theoretical point of view. This statement also applies to the numeric value and range described above.

Hereinafter, embodiments of the present invention are explained in detail on the basis of the drawings. In all the drawings for explaining embodiments, the same symbol is attached to the member having the same function, as a principle, and the repeated explanation is omitted. In the embodiments below, the explanation for the same or a similar part is not repeated in principle, except for cases requiring an explanation in particular.

In drawings used in embodiments, to make the drawing intelligible, hatching may be omitted even if it is a cross-sectional view. Moreover, to make the drawing intelligible, hatching may be attached even if it is a plan view.

Embodiment 1

The present invention is a semiconductor device including a nonvolatile memory (a nonvolatile memory device, a flash memory, a nonvolatile semiconductor memory device), and the nonvolatile memory uses a trapping insulating film (an insulating film capable of accumulating electric charges) mainly in an electric charge accumulation part. In the embodiment below, the nonvolatile memory is explained based on a memory cell on the basis of an n-channel type MISFET (Metal Insulator Semiconductor Field Effect Transistor) using the trapping insulating film. Polarity (polarity of an applied voltage in write/erase/read, or polarity of a carrier) in the embodiment below is for explaining the operation in the case of a memory cell on the basis of the n-channel type MISFET, and, when the memory cell is based on a p-channel type MISFET, it is possible to obtain the same operation, in principle, by reversing all the polarities of the applied potential, the conductivity type of the carrier.

The semiconductor device of the embodiment is explained with reference to the drawings.

FIG. 1 is a cross-sectional view of essential parts of the semiconductor device in the embodiment. The semiconductor device in the embodiment is a semiconductor device including a nonvolatile memory. FIG. 1 shows a cross-sectional view of essential parts of a memory cell region of the nonvolatile memory. FIG. 2 is a partially enlarged cross-sectional view (a cross-sectional view of essential parts) of a memory cell MC of the semiconductor device in the embodiment, and a part of FIG. 1 is enlarged. FIG. 3 is an equivalent circuit diagram of the memory cell MC. In FIG. 2, to make the drawing intelligible, illustration of an interlayer insulating film 22 shown in FIG. 1 is omitted.

As shown in FIG. 1, for a semiconductor substrate (a semiconductor wafer) 1 including a p-type single crystalline silicon having a specific resistance of around 1 to 10 Ωcm, an element isolation region (which corresponds to an element isolation region 2 described later, but is not shown here) for isolating elements is formed, and, in an active region isolated (defined) by the element isolation region, a p-type well PW1 is formed. For the p-type well PW1 in the memory cell region, the memory cell MC of nonvolatile memory including a memory transistor and a control transistor (selection transistor) as shown in FIG. 1 is formed. In each of the memory cell regions, actually, a plurality of memory cells MC is formed in an array, and FIG. 1 shows a cross section of one memory cell MC among these. Each memory cell region is isolated electrically from other regions by the element isolation region.

As shown in FIGS. 1 to 3, the memory cell MC of the nonvolatile memory of the semiconductor device in the embodiment is a split gate type memory cell, in which two MISFETs of a control transistor (selection transistor) having a control gate electrode (a selection gate electrode) CG and a memory transistor having a memory gate electrode (a gate electrode for a memory) MG are connected.

A MISFET (Metal Insulator Semiconductor Field Effect Transistor) including a gate insulating film including an electric charge accumulation part (an electric charge accumulation layer), and a memory gate electrode MG is called a memory transistor (a transistor for memory), and a MISFET including the gate insulating film and the control gate electrode CG is called a control transistor (a selection transistor, a transistor for selecting a memory cell). Accordingly, the memory gate electrode MG is the gate electrode of a memory transistor, the control gate electrode CG is the gate electrode of a control transistor, and the control gate electrode CG and the memory gate electrode MG are gate electrodes constituting the nonvolatile memory (its memory cell).

Hereinafter, the structure of the memory cell MC is explained specifically.

As shown in FIGS. 1 and 2, the memory cell MC of the nonvolatile memory has n-type semiconductor regions MS and MD for a source and a drain, formed in a p-type well PW1 of the semiconductor substrate 1, the control gate electrode CG formed in an upper part of the semiconductor substrate 1 (the p-type well PW1), and the memory gate electrode MG that is formed in an upper part of the semiconductor substrate 1 (the p-type well PW1) and is adjacent to the control gate electrode CG. And, the memory cell MC of the nonvolatile memory furthermore has an insulating film (a gate insulating film) 3 formed between the control gate electrode CG and the semiconductor substrate 1 (the p-type well PW1), and an insulating film 5 formed between the memory gate electrode MG and the semiconductor substrate 1 (the p-type well PW1), and between the memory gate electrode MG and the control gate electrode CG.

The control gate electrode CG and the memory gate electrode MG extend along the main surface of the semiconductor substrate 1, and are arranged side by side, with the insulating film 5 interposed between the opposing side surfaces (side walls) of these electrodes. The extending direction of the control gate electrode CG and the memory gate electrode MG is the direction perpendicular to the plane of paper of FIG. 1. The control gate electrode CG and the memory gate electrode MG are formed in the upper part of the semiconductor substrate 1 (the p-type well PW1) between the semiconductor region MD and the semiconductor region MS via the insulating films 3 and 5 (the control gate electrode CG is formed via the insulating film 3, and the memory gate electrode MG is formed via the insulating film 5). The memory gate electrode MG is located on the semiconductor region MS side and the control gate electrode CG is located on the semiconductor region MD side.

The control gate electrode CG and the memory gate electrode MG are adjacent to each other with the insulating film 5 interposed between them, and the memory gate electrode MG is formed in a sidewall spacer shape over the side surface (the side wall) of the control gate electrode CG via the insulating film 5. The insulating film 5 extends over both regions of a region between the memory gate electrode MG and the semiconductor substrate 1 (the p-type well PW1), and a region between the memory gate electrode MG and the control gate electrode CG.

The insulating film 3 formed between the control gate electrode CG and the semiconductor substrate 1 (the p-type well PW1) (the insulating film 3 under the control gate electrode CG) functions as the gate insulating film of the control transistor, and the insulating film 5 between the memory gate electrode MG and the semiconductor substrate 1 (the p-type well PW1) (the insulating film 5 under the memory gate electrode MG) functions as the gate insulating film of the memory transistor (a gate insulating film including an electric charge accumulation part).

In the embodiment, the insulating film 3 is a high-permittivity film having a permittivity (a relative permittivity) higher than that of a silicon nitride film (a High-k film). In the application, a High-k film, high-permittivity film or a high-permittivity gate insulating film means a film having a permittivity (a relative permittivity) higher than that of silicon nitride film. A metal oxide film such as a hafnium oxide film, a zirconium oxide film, an aluminum oxide film, a tantalum oxide film, or a lanthanum oxide film may be used as the insulating film 3.

The insulating film 3 being a high-permittivity film may be formed directly on the surface (the silicon surface) of the semiconductor substrate 1 (the p-type well PW1) (an interface layer 3 a is omitted), or, as shown in FIG. 2, the insulating interface layer (an insulating layer, insulating film) 3 a including a silicon oxide film or a silicon oxynitride film may be provided at the interface between the insulating film 3 being a high-permittivity film and the semiconductor substrate 1 (the p-type well PW1). By providing the interface layer 3 a including silicon oxide or silicon oxynitride, it is possible to form the interface between the gate insulating film and the semiconductor substrate (the silicon surface thereof) of the control transistor to an SiO₂/Si (or SiON/Si) structure, to reduce a number of defects such as traps, and to improve driving capability and reliability.

The insulating film 5 includes a stacked film having a silicon oxide film (an oxide film) 5 a, a silicon nitride film (a nitride film, electric charge accumulation layer) 5 b over the silicon oxide film 5 a, and a silicon oxide film (an oxide film) 5 c over the silicon nitride film 5 b.

In FIG. 1, to make the drawing intelligible, the stacked film of the silicon oxide film 5 a, the silicon nitride film 5 b and the silicon oxide film 5 c is shown simply as the insulating film 5. But, actually, as shown in FIG. 2, the insulating film 5 includes the stacked film of the silicon oxide film 5 a, the silicon nitride film 5 b over the silicon oxide film 5 a, and the silicon oxide film 5 c over the silicon nitride film 5 b.

Because the insulating film 5 has the stacked structure of the silicon oxide film 5 a, the silicon nitride film 5 b and the silicon oxide film 5 c, the insulating film 5 extending in the region between the memory gate electrode MG and the semiconductor substrate 1 (the p-type well PW1) and the region between the memory gate electrode MG and the control gate electrode CG may be considered as a stacked gate insulating film (a gate insulating film of a stacked structure). The insulating film 5 between the memory gate electrode MG and the semiconductor substrate 1 (the p-type well PW1) functions as the gate insulating film of the memory transistor, and the insulating film 5 between the memory gate electrode MG and the control gate electrode CG functions as an insulating film for insulating (isolating electrically) between the memory gate electrode MG and the control gate electrode CG.

In the insulating film 5, the silicon nitride film 5 b is an insulating film for accumulating electric charges, and functions as an electric charge accumulation layer (an electric charge accumulation part). The silicon nitride film 5 b is a trapping insulating film formed in the insulating film 5. Consequently, the insulating film 5 may be considered as an insulating film including the electric charge accumulation part (the electric charge accumulation layer, the silicon nitride film 5 b).

The silicon oxide film 5 c and the silicon oxide film 5 a located over and below the silicon nitride film 5 b can function as an electric charge blocking layer (an electric charge blocking film, electric charge confinement layer). The structure of sandwiching the silicon nitride film 5 b with the silicon oxide film 5 c and the silicon oxide film 5 a enables the accumulation of electric charges in the silicon nitride film 5 b. The silicon oxide film 5 a, the silicon nitride film 5 b and the silicon oxide film 5 c may also be considered as an ONO (oxide-nitride-oxide) film.

As a modification, as shown in FIG. 4, it is also possible to form the insulating film 5 as a stacked film of the silicon oxide film 5 a, the silicon nitride film (the electric charge accumulation layer) 5 b over the silicon oxide film 5 a, the silicon oxide film 5 c over the silicon nitride film 5 b, and an insulating film 5 d over the silicon oxide film 5 c, and to set the insulating film 5 d of the uppermost layer to be a high-permittivity film (a High-k film) having a permittivity (a relative permittivity) higher than that of a silicon nitride film. FIG. 4 is a cross-sectional view of essential parts showing the modification of the semiconductor device in the embodiment, and shows a cross-sectional region corresponding to that in FIG. 2. A metal oxide film such as a hafnium oxide film, a zirconium oxide film, an aluminum oxide film, a tantalum oxide film or a lanthanum oxide film may be used as the insulating film 5 d.

The semiconductor region MS is a semiconductor region functioning as one of a source region and a drain region, and the semiconductor region MD is a semiconductor region functioning as the other of the source region and the drain region. The semiconductor region MS is a semiconductor region functioning as the source region, and the semiconductor region MD is a semiconductor region functioning as the drain region. The semiconductor regions MS and MD include a semiconductor region into which an n-type impurity has been introduced (an n-type impurity diffusion layer), and each has an LDD (lightly doped drain) structure. The semiconductor region MS for the source has an n⁻-type semiconductor region 7 a and an n⁺-type semiconductor region 8 a having an impurity concentration higher than that of the n⁻-type semiconductor region 7 a, and the semiconductor region MD for the drain has an n⁻-type semiconductor region 7 b and an n⁺-type semiconductor region 8 b having an impurity concentration higher than that of the n⁻-type semiconductor region 7 b. The n⁺-type semiconductor region 8 a is deeper in a junction depth and higher in the impurity concentration than the n⁻-type semiconductor region 7 a, and the n⁺-type semiconductor region 8 b is deeper in the junction depth and higher in the impurity concentration than the n⁻-type semiconductor region 7 b.

Over the side walls of the memory gate electrode MG and the control gate electrode CG (side walls on the sides that are not adjacent to each other), a sidewall spacer (a sidewall, a side wall insulating film) SW including an insulating film (a silicon oxide film, a silicon nitride film, or a stacked film of these films) is formed. The sidewall spacer SW is formed over the side wall (the side surface) of the memory gate electrode MG on the other side of the side adjacent to the control gate electrode CG via the insulating film 5, and over the side wall (the side surface) of the control gate electrode CG on the other side of the side adjacent to the memory gate electrode MG via the insulating film 5.

Out of the side walls (the side surfaces) of the control gate electrode CG, the side wall (the side surface) on the side adjacent to the memory gate electrode MG via the insulating film 5 shall be given a symbol 11 a to be referred to as a side wall (a side surface) 11 a, and the side wall (the side surface) on the other side of the side adjacent to the memory gate electrode MG via the insulating film 5 shall be given a symbol 11 b to be referred to as a side wall (a side surface) 11 b. The side wall 11 a and the side wall 11 b of the control gate electrode CG are located on the sides opposite to each other. Moreover, out of the side walls (the side surfaces) of the memory gate electrode MG, the side wall (the side surface) on the side adjacent to the control gate electrode CG via the insulating film 5 shall be given a symbol 12 a to be referred to as a side wall (a side surface) 12 a, and the side wall (the side surface) on the other side of the side adjacent to the control gate electrode CG via the insulating film 5 shall be given a symbol 12 b to be referred to as a side wall (a side surface) 12 b. The side wall 12 a and the side wall 12 b of the memory gate electrode MG are located on the sides opposite to each other. The sidewall spacer SW formed over the side wall (the side surface) 12 b of the memory gate electrode MG shall be given a symbol SW1 to be referred to as a sidewall spacer SW1. The sidewall spacer SW formed over the side wall (the side surface) 11 b of the control gate electrode CG shall be given a symbol SW2 to be referred to as a sidewall spacer SW2.

The sidewall spacer SW1 is formed over the side wall 12 b of the memory gate electrode MG. The sidewall spacer SW1 is not formed directly on the side wall 12 b of the memory gate electrode MG, but formed over the side wall 12 b of the memory gate electrode MG via the side wall insulating film 14 a. The side wall insulating film 14 a is formed over the side wall 12 b of the memory gate electrode MG, and the sidewall spacer SW1 is formed over the side wall 12 b of the memory gate electrode MG via the side wall insulating film 14 a. The sidewall spacer SW2 is formed over the side wall 11 b of the control gate electrode CG. The sidewall spacer SW2 is not formed directly on the side wall 11 b of the control gate electrode CG, but formed over the side wall 11 b of the control gate electrode CG via the side wall insulating film 14 b. The side wall insulating film 14 b is formed over the side wall 11 b of the control gate electrode CG, and the sidewall spacer SW2 is formed over the side wall 11 b of the memory gate electrode MG via the side wall insulating film 14 b. The side wall insulating film 14 a is interposed between the memory gate electrode MG (its side wall 12 b) and the sidewall spacer SW1. The side wall insulating film 14 b is interposed between the control gate electrode CG (its side wall 11 b) and the sidewall spacer SW2.

Over the side wall 11 a of the control gate electrode CG, the side wall insulating film 13 a is formed. Between the memory gate electrode MG (its side wall 12 a) and the control gate electrode CG (its side wall 11 a), the side wall insulating film 13 a and the insulating film 5 are interposed. The side wall insulating film 13 a is interposed between a part of the insulating film 5 located between the memory gate electrode MG (its side wall 12 a) and the control gate electrode CG (its side wall 11 a), and the control gate electrode CG (its side wall 11 a). Between the memory gate electrode MG (its side wall 12 a) and the control gate electrode CG (its side wall 11 a), the side wall insulating film 13 a and the insulating film 5 are stacked in the order from the control gate electrode CG side. The side wall insulating film 13 a is not formed between the memory gate electrode MG (its lower surface) and the semiconductor substrate 1 (the p-type well PW1). The insulating film 5 also extends between the memory gate electrode MG (its lower surface) and the semiconductor substrate 1 (the p-type well PW1)

The n⁻-type semiconductor region 7 a of the source part is formed by self-alignment technique for the side surface of the side wall insulating film 14 a over the side wall 12 b of the memory gate electrode MG (the side surface on the side opposite to the side in contact with the memory gate electrode MG), and the n⁺-type semiconductor region 8 a is formed by self-alignment technique for the side surface of the sidewall spacer SW1 (the side surface on the side opposite to the side in contact with the side wall insulating film 14 a). Consequently, the low-concentration n⁻-type semiconductor region 7 a is formed under (below) the sidewall spacer SW1 over the side wall of the memory gate electrode MG, and the high-concentration n⁺-type semiconductor region 8 a is formed outside the low-concentration n⁻-type semiconductor region 7 a. Accordingly, the low-concentration n⁻-type semiconductor region 7 a is formed to be adjacent to a channel region of the memory transistor, and the high-concentration n⁺-type semiconductor region 8 a is formed to contact (is adjacent to) the low-concentration n⁻-type semiconductor region 7 a to be separated from the channel region of the memory transistor by the portion of the n⁻-type semiconductor region 7 a.

The n⁻-type semiconductor region 7 b of the drain part is formed by self-alignment technique for the side surface of the side wall insulating film 14 b over the side wall of the control gate electrode CG (the side surface on the side opposite to the side in contact with the control gate electrode CG), and the n⁺-type semiconductor region 8 b is formed by self-alignment technique for the side surface of the sidewall spacer SW2 (the side surface on the side opposite to the side in contact with the side wall insulating film 14 b). Consequently, the low-concentration type semiconductor region 7 b is formed under (below) the sidewall spacer SW2 over the side wall of the control gate electrode CG, and the high-concentration n⁺-type semiconductor region 8 b is formed outside the low-concentration n⁻-type semiconductor region 7 b. Accordingly, the low-concentration type semiconductor region 7 b is formed to be adjacent to the channel region of the control transistor, and the high-concentration n⁺-type semiconductor region 8 b is formed to contact (is adjacent to) the low-concentration n⁻-type semiconductor region 7 b to be separated from the channel region of the memory transistor by the portion of the n⁻-type semiconductor region 7 b.

The channel region of the memory transistor is formed under the insulating film 5 under the memory gate electrode MG, and that of the control transistor is formed under the insulating film 3 under the control gate electrode CG.

For the n⁻-type semiconductor region 7 b of the drain part, a halo region HA for suppressing short-channel characteristics (punch through) is formed. In the p-type well PW1, the halo region HA is formed to encompass (cover) the n⁻-type semiconductor region 7 b. The halo region HA has an inverse conductivity type with respect to the n⁻-type semiconductor region 7 b, has the same conductivity type as that of the p-type well PW1, has an impurity, concentration (p type impurity concentration) higher than that of the p-type well PW1, and is of a p-type (a p-type semiconductor region).

The halo region HA is formed for the n⁻-type semiconductor region 7 b for the drain (is formed to encompass the n⁻-type semiconductor region 7 b in the p-type well PW1), and is formed for suppressing the short-channel characteristics of the control transistor. The halo region HA may not be formed for the n⁻-type semiconductor region 7 a for the source, but may also be formed for suppressing the short-channel characteristics of the memory transistor.

The control gate electrode CG includes a conductor (a conductor film). In the embodiment, the control gate electrode CG is formed from a metal film 4 a and a silicon film 4 b over the metal film 4 a. The control gate electrode CG is constituted by a stacked film (a stacked structure) of the metal film (a metal layer, a metal gate film) 4 a in contact with the gate insulating film (the insulating film 3 being a high-permittivity gate insulating film) and the silicon film 4 b over the metal film 4 a. Specifically, the control gate electrode CG includes the patterned stacked film of the metal film 4 a and the silicon film 4 b. The control gate electrode CG has the metal film 4 a in contact with the gate insulating film (the insulating film 3 being a high-permittivity gate insulating film), and therefore it is a metal gate electrode. The metal film 4 a is a conductor film showing metallic conduction. An aluminum (Al) film, a titanium (Ti) film, a zirconium (Zr) film, a lanthanum (La) film, or other films may be used. The silicon film 4 b is preferably a doped polysilicon film (a polycrystalline silicon film into which an impurity has been introduced), and is made to have a low resistivity by the introduction of an impurity (an n-type impurity).

The memory gate electrode MG is formed from a stacked film of a metal film (a metal layer, a metal gate film) 6 a and a silicon film 6 b over the metal film 6 a. The metal film 6 a constituting the memory gate electrode MG contacts the insulating film 5, and the silicon film 6 b constituting the memory gate electrode MG does not contact the insulating film 5. The metal film 6 a constituting the memory gate electrode MG is interposed between the silicon film 6 b constituting the memory gate electrode MG and the insulating film 5. The insulating film 5 and the metal film 6 a of the memory gate electrode MG are interposed between the silicon film 6 b of the memory gate electrode MG and the semiconductor substrate 1 (the p-type well PW1). The side wall insulating film 13 a, the insulating film 5 and the metal film 6 a of the memory gate electrode MG are interposed between the silicon film 6 b of the memory gate electrode MG and the control gate electrode CG. The memory gate electrode MG has the metal film 6 a in contact with the insulating film 5 of a portion located between the memory gate electrode MG and the semiconductor substrate 1 (the p-type well PW1), and it is a metal gate electrode. The metal film 6 a is a conductor film showing metallic conduction, and in particular, one capable of being oxidized is furthermore advantageous. For example, an aluminum (Al) film, a titanium (Ti) film, a zirconium (Zr) film, a lanthanum (La) film, or other films may be used. The silicon film 6 b is preferably a doped polysilicon film (a polycrystalline silicon film into which an impurity has been introduced), and is made to have a low resistivity by the introduction of an impurity (an n-type impurity).

On an upper end part 16 a side of the metal film 6 a constituting the memory gate electrode MG, a metal oxide portion 17 having insulating properties is formed. The metal oxide portion 17 is formed by oxidation of a part of the metal film 6 a, and the upper end part 16 a of the metal film 6 a is adjacent to (in contact with) the metal oxide portion 17. The metal oxide portion 17 is formed continuously to the metal film 6 a over the upper end part 16 a of the metal film 6 a. Consequently, the upper end part of the metal film 6 a has been oxidized to form the metal oxide portion 17 in the upper end part of the metal film 6 a. Because the metal oxide portion 17 is formed by the oxidation of a part of the metal film 6 a, the metal element constituting the metal oxide portion 17 is the same as the metal element constituting the metal film 6 a. When the metal film 6 a is an aluminum (Al) film, the metal oxide portion 17 includes aluminum oxide. Moreover, because the upper end part of the metal film 6 a is oxidized to form the metal oxide portion 17, the metal oxide portion 17 is sandwiched vertically by the interlayer insulating film 22 and metal film 6 a, and is sandwiched horizontally (in a gate length direction) by the silicon film 6 b constituting the memory gate electrode MG, a metal silicide layer 21 a formed in an upper part of the silicon film 6 b, and the insulating film 5. The metal oxide portion 17 is surrounded by the silicon film 6 b constituting the memory gate electrode MG, the metal silicide layer 21 a formed in the upper part of the silicon film 6 b, the metal film 6 a, the insulating film 5, and the interlayer insulating film 22.

A side end part 16 b of the metal film 6 a constituting the memory gate electrode MG is adjacent to (in contact with) the side wall insulating film 14 a formed over the side wall 12 b of the memory gate electrode MG, and has scarcely been oxidized. The upper end part 16 a and the side end part 16 b of the metal film 6 a constituting the memory gate electrode MG are located on sides opposite to each other in the metal film 6 a extending from between the control gate electrode CG and the memory gate electrode MG to between the memory gate electrode MG and the semiconductor substrate 1. In the metal film 6 a extending in a direction parallel to the semiconductor substrate 1 with a prescribed thickness, the end part on a side exposed from the side wall 12 b of the memory gate electrode MG is called the side end part 16 b of the metal film 6 a. In the metal film 6 a extending in a direction parallel to the side wall 11 a of the control gate electrode CG with a prescribed thickness over the side wall 11 a of the control gate electrode CG, the end part located on the upper part side of the memory gate electrode MG is called the upper end part 16 a of the metal film 6 a.

In an upper part (an upper surface) of the silicon film 6 b constituting the memory gate electrode MG, an upper part (an upper surface) of the silicon film 4 b constituting the control gate electrode CG, and upper parts (upper surfaces, surfaces) of the n⁺-type semiconductor regions 8 a and 8 b, the metal silicide layer (metal silicide film) 21 is formed by a Salicide (Self Aligned Silicide) technology. The metal silicide layer 21 includes a cobalt silicide layer, a nickel silicide layer, and a platinum-added nickel silicide layer. The metal silicide layer 21 can lower diffusion resistance and contact resistance. The metal silicide layer 21 formed in the upper part (the upper surface) of the silicon film 6 b constituting the memory gate electrode MG shall be given a symbol 21 a to be called a metal silicide layer 21 a. The metal silicide layer 21 formed in the upper part (the upper surface) of the silicon film 4 b constituting the control gate electrode CG shall be given a symbol 21 b to be called a metal silicide layer 21 b. The metal film 4 a and the silicon film 4 b constituting the control gate electrode CG together with the metal silicide layer 21 b in the upper part of the silicon film 4 b collectively may also be considered as the control gate electrode CG, and the metal film 6 a and the silicon film 6 b constituting the memory gate electrode MG together with the metal silicide layer 21 a in the upper part of the silicon film 6 b collectively may also be considered as the memory gate electrode MG. The metal film 6 a and the silicon film 6 b constituting the memory gate electrode MG together with the metal silicide layer 21 a in the upper part of the silicon film 6 b, and the metal oxide portion 17 in the upper end part of the metal film 6 a collectively may also be considered as the memory gate electrode MG (as described above, the metal oxide portion 17 has insulating properties). From the viewpoint of preventing short circuit between the memory gate electrode MG and the control gate electrode CG as far as possible, no metal silicide layer 21 may not be formed in the upper part of one or both of the memory gate electrode MG and the control gate electrode CG.

Over the semiconductor substrate 1, the memory gate electrode MG and the sidewall spacer SW, the interlayer insulating film 22 is formed as an insulating film to cover the control gate electrode CG, the memory gate electrode MG and the sidewall spacer SW. The interlayer insulating film 22 includes a single film of a silicon oxide film, and a stacked film of a silicon nitride film and a silicon oxide film formed over the silicon nitride film, which is thicker than the silicon nitride film. The upper surface of the interlayer insulating film 22 is planarized.

In the interlayer insulating film 22, a contact hole (an opening part, a through hole) CNT is formed. In the contact hole CNT, an electroconductive plug PG is embedded as a conductor part (a conductor part for connection).

The plug PG is formed from a thin barrier conductor film formed over the bottom part and the side wall (the side surface) of the contact hole CNT, and a main conductor film formed to be embedded in the contact hole CNT over the barrier conductor film. To simplify the drawing, FIG. 1 shows the barrier conductor film and the main conductor film constituting the plug PG integrally. The barrier conductor film constituting the plug PG may be a titanium film, a titanium nitride film, or a stacked film of these film. The main conductor film constituting the plug PG may be a tungsten film.

The contact hole CNT and the plug PG embedded in the contact hole CNN are formed in the upper part of the n⁺-type semiconductor regions 8 a and 8 b, the control gate electrode CG, the memory gate electrode MG, and other places. In the bottom part of the contact hole CNT, a part of the main surface of the semiconductor substrate 1, such as a part of the n⁺-type semiconductor regions 8 a and 8 b (the metal silicide layer 21 over the surface of the n⁺-type semiconductor regions 8 a and 8 b), a part of the control gate electrode CG (the metal silicide layer 21 over the surface of the control gate electrode CG), a part of the memory gate electrode MG (the metal silicide layer 21 over the surface of the memory gate electrode MG), is exposed. And, to the exposed part (the exposed part in the bottom part of the contact hole CNT), the plug PG is connected. FIG. 1 shows a cross section in which a part of the n⁺-type semiconductor region 8 b (the metal silicide layer 21 over the surface of the n⁺-type semiconductor region 8 b) is exposed in the bottom part of the contact hole CNT and is connected electrically with the plug PG embedded in the contact hole CNT.

Over the interlayer insulating film 22 in which the plug PG is embedded, wiring (a wiring layer) M1 is formed. The wiring M1 is a damascene wiring (embedded wiring), and is embedded in a wiring trench provided in an insulating film formed over the interlayer insulating film 22 (although not shown in FIG. 1, it corresponds to an insulating film 24 described later). The wiring M1 is connected electrically with the source region of the memory transistor (the semiconductor region MS), the drain region of the control transistor (the semiconductor region MD), the control gate electrode CG, the memory gate electrode MG or the like via the plug PG. FIG. 1 shows, as a wiring M1, the wiring M1 connected electrically with the drain region of the control transistor (the semiconductor region MD) via the plug PG. Although a wiring and an insulating film of a furthermore upper layer are also formed, the illustration and the explanation are omitted. The wiring M1 and a wiring in a layer upper than the wiring M1 are not limited to a damascene wiring (an embedded wiring), but may be formed by patterning a conductor film for wiring. The wiring may be a tungsten wiring, an aluminum wiring, or other wiring.

FIG. 5 is a table showing an example of application conditions of a voltage to each site of a selection memory cell in “WRITE,” “ERASE” and “READ” in the embodiment. The table in FIG. 5 describes a voltage Vmg applied to the memory gate electrode MG, a voltage Vs applied to the source region (the semiconductor region MS), a voltage Vcg applied to the control gate electrode CG, a voltage Vd applied to the drain region (the semiconductor region MD), and a voltage Vb applied to the p-type well PW1 of the memory cell (the selection memory cell) in FIGS. 1 to 3, in each of “WRITE,” “ERASE” and “READ.” The table in FIG. 5 shows a favorable application condition of the voltage, and the condition is not limited to this but can change as needed. In the embodiment, “WRITE” is defined as injection of an electron into the silicon nitride film 5 b being the electric charge accumulation layer (the electric charge accumulation part) in the insulating film 5 of the memory transistor, and “ERASE” is defined as injection of a hole.

Hot electron write, which is called SSI (Source Side Injection) system, can be used as a write system. For example, the voltage shown in a column of “WRITE” in FIG. 5 is applied to each site of the selection memory cell for which the write is performed to inject an electron in the silicon nitride film 5 b in the insulating film 5 of the selection memory cell. The hot electron is generated in the channel region (between the source and drain) under between two gate electrodes (the memory gate electrode MG and the control gate electrode CG) and then injected into the silicon nitride film 5 b being the electric charge accumulation layer (the electric charge accumulation part) in the insulating film 5 under the memory gate electrode MG. The injected hot electron (electron) is trapped at a trap level in the silicon nitride film 5 b in the insulating film 5. Consequently, a threshold voltage of the memory transistor rises.

A BTBT (Band-To-Band Tunneling) hot hole injection erase system can be used as the erase method. Erase is performed by injecting the hole generated by the BTBT (Band-To-Band Tunneling) into the electric charge accumulation part (the silicon nitride film 5 b in the insulating film 5). The voltage in a column of “ERASE” in FIG. 5 is applied to each site of the selection memory cell for which erase is performed to generate a hole by a BTBT (Band-To-Band Tunneling) phenomenon. Then, the hole is accelerated by electric field to be injected into the silicon nitride film 5 b in the insulating film 5 in the selection memory cell. Consequently, the threshold voltage of the memory transistor lowers.

In read, a voltage in the column of “READ” in FIG. 5 is applied to respective sites of the selection memory cell from which the read is performed. By setting the voltage Vmg applied to the memory gate electrode MG in read to a value between the threshold voltage of the memory transistor in a write state and that of the memory transistor in an erase state, the write state can be discriminated from the erase state.

Next, a method of manufacturing the semiconductor device in the embodiment is explained.

FIGS. 6 and 7 are process flow charts showing a part of the process of manufacturing a semiconductor device in the embodiment. FIGS. 8 to 33 are cross-sectional views of essential parts in the process of manufacturing a semiconductor device in the embodiment. Among these, cross-sectional views in FIGS. 8 to 15 and 18 to 33 show cross-sectional views of essential parts of a memory cell region (a region in which the memory cell MC of the nonvolatile memory is formed) 1A and a peripheral circuit region (a region in which a circuit other than the nonvolatile memory is formed) 1B, and show how the memory cell MC is formed in the memory cell region 1A and the MISFET is formed in the peripheral circuit region 1B. FIGS. 16 and 17 correspond to the partially enlarged cross-sectional view of FIG. 15. The memory cell region 1A and the peripheral circuit region 1B are formed in the same semiconductor substrate 1. The memory cell region 1A and the peripheral circuit region 1B may not be adjacent to each other. But, for easy understanding, in cross-sectional views in FIGS. 8 to 15 and 18 to 33, the peripheral circuit region 1B is next to the memory cell region 1A. The peripheral circuit means a circuit other than the nonvolatile memory, and includes processors such as a CPU, a controlling circuit, a sense amplifier, a column decoder, a row decoder, and an input/output circuit. The MISFET formed in the peripheral circuit region 1B is a MISFET for the peripheral circuit.

In the embodiment, n-channel type MISFETs (the control transistor and the memory transistor) are formed in the memory cell region 1A, but, p-channel type MISFETs (the control transistor and the memory transistor) may be formed in the memory cell region 1A by reversing the conductivity type. Similarly in the embodiment, n-channel type MISFETs are formed in the peripheral circuit region 1B is explained, but p-channel type MISFETs may be formed in the peripheral circuit region 1B by reversing the conductivity type. Also, a CMISFET (a Complementary MISFET) may also be formed in the peripheral circuit region 1B.

As shown in FIG. 8, first, the semiconductor substrate (the semiconductor wafer) 1 including a p-type single crystalline silicon having a specific resistance of around 1 to 10 Ωcm is provided (prepared) (Step S1 in FIG. 6). Next, in the main surface of the semiconductor substrate 1, the element isolation region (an inter-element isolation insulating region) 2 defining (demarcating) an active region is formed (Step S2 in FIG. 6). The element isolation region 2 includes an insulator such as silicon oxide, and can be formed by an STI (Shallow Trench Isolation) process or a LOCOS (Local Oxidization of Silicon) process. The element isolation region 2 may be formed by forming a trench for element isolation in the main surface of the semiconductor substrate 1 and then by embedding the trench for element isolation with an insulating film including silicon oxide.

Next, as shown in FIG. 9, a p-type well PW1 is formed in the memory cell region 1A of the semiconductor substrate 1, and a p-type well PW2 is formed in the peripheral circuit region 1B (Step S3 in FIG. 6). The p-type wells PW1 and PW2 can be formed by ion implantation of a p-type impurity such as boron (B) into the semiconductor substrate 1. The p-type wells PW1 and PW2 are formed over a prescribed depth from the main surface of the semiconductor substrate 1.

In the embodiment, it is desirable not to perform channel dope ion implantation for the memory cell region 1A (the p-type well PW1) of the semiconductor substrate 1. Or, even when performing the channel dope ion implantation, it is preferable to make a dose amount small to lower the impurity concentration in the channel region. The channel dope ion implantation is, generally, an ion implantation for adjusting the threshold value of a transistor, and is performed for introducing (doping) an impurity into a region to be the channel region of the transistor later. In the embodiment, by not performing the channel dope ion implantation for introducing (doping) an impurity into a region to be the channel region of, the control transistor or the memory transistor later, or, even when performing the channel dope ion implantation, by making the dose amount small, it is possible to lower the impurity concentration in the channel region of the control transistor and the memory transistor.

Next, by wet etching using a hydrofluoric acid (HF) solution, a natural oxide film on the surface of the semiconductor substrate 1 is removed and then the surface of the semiconductor substrate 1 is cleaned (washed). Consequently, the surface (the silicon surface) of the semiconductor substrate 1 (the p-type wells PW1 and PW2) is exposed.

Next, over the main surface of the semiconductor substrate 1 (the surfaces of the p-type wells PW1 and PW2), the insulating film 3 is formed (Step S4 in FIG. 6). The insulating film 3 is, as described above, high-permittivity film (a High-k film), and the usable materials are as described above. The insulating film 3 can be formed using a sputtering process, an ALD (Atomic Layer Deposition) process, a CVD (Chemical, Vapor Deposition) process, or the like. The thickness of the insulating film 3 may be set to around from 0.5 to 3.0 nm.

Prior to forming the insulating film 3, it is possible to form the interface layer 3 a including a silicon oxide film or a silicon oxynitride film over the surface of the semiconductor substrate 1 (the surfaces of the p-type wells PW1 and PW2) using a thermal oxidation process and then to form the insulating film 3 over the interface layer 3 a (FIG. 9 does not show the interface layer 3 a). When the interface layer 3 a is formed, the insulating film 3 is formed over the interface layer 3 a. Because the interface layer 3 a is not formed over the element isolation region 2, the insulating film 3 is formed directly on the element isolation region 2. When the interface layer 3 a is formed and then the insulating film 3 is formed over the interface layer 3 a, it is possible to reduce the number of defects such as traps and then to improve driving capability and reliability. When the interface layer 3 a is formed, the thickness of the interface layer 3 a may be as small as from 0.5 to 3.0 nm.

Next, as shown in FIG. 10, over the main surface (the whole main surface) of the semiconductor substrate 1 (over the insulating film 3), a metal film (a metal layer, a metal gate film) 4 a for a metal gate (a metal gate electrode) is formed (deposited) (Step S5 in FIG. 6). Favorable materials as the metal film 4 a are as described above. The metal film 4 a may be formed by a sputtering process or the like. The thickness of the metal film 4 a (formed film thickness) may be around from 10 to 20 nm.

Next, as shown in FIG. 11, over the main surface (the whole main surface) of the semiconductor substrate 1 (over the metal film 4 a), a silicon film 4 b is formed (deposited) (Step S6 in FIG. 6).

The silicon film 4 b includes a polycrystalline silicon film (a polysilicon film), and can be formed using a CVD process or the like. The thickness of the silicon film 4 b (deposited film thickness) may be around from 50 to 200 nm. It is possible to form the silicon film 4 b as an amorphous silicon film in film forming and then to form the amorphous silicon film into a polycrystalline silicon film by a subsequent heat treatment.

The silicon film 4 b is more preferable if it has a low resistivity by introducing an impurity (an n-type impurity such as phosphorus (P) or arsenic (As), or a p-type impurity such as boron (B)). The impurity can be introduced in or after forming the silicon film 4 b. When the impurity is introduced in forming the silicon film, by including a doping gas (a gas for adding an impurity) in a gas for forming the silicon film 4 b, the silicon film 4 b into which the impurity has been introduced can be formed. When an impurity is introduced after forming the silicon film, after forming the silicon film without introducing intentionally an impurity, an impurity is introduced into the silicon film by an ion implantation process or the like and then it is possible to form the silicon film 4 b into which the impurity has been introduced.

Although it is also possible to omit the step of forming the silicon film 4 b of Step S6 (the step of forming the control gate electrode CG by the metal film 4 a without the silicon film 4 b) by increasing the thickness of the metal film 4 a formed in Step S5, it is more preferable to form the silicon film 4 b over the metal film 4 a in Step S6 (to form the control gate electrode CG by a stacked film of the metal film 4 a and the silicon film 4 b over the metal film 4A). The reason is that the metal film 4 a having too large a thickness may cause such problems that the metal film 4 a is easily peeled off or the substrate is damaged by overetching in patterning the metal film 4 a, but that, by forming the control gate electrode CG by the stacked film of the metal film 4 a and the silicon film 4 b, the thickness of the metal film 4 a can be decreased as compared with the case of forming the control gate electrode CG only with the metal film 4 a, thus improving the above-mentioned problems. Moreover, when the silicon film 4 b is formed over the metal film 4 a, traditional processing methods and processes of polysilicon gate electrodes (gate electrodes made of polysilicon) can be followed. This is advantageous in terms of fine processing properties, manufacturing cost, and yield. Hereinafter, the stacked film of the metal film 4 a and the silicon film 4 b over the metal film 4 a is called a stacked film 4.

Next, the stacked film 4 (the stacked film 4 of the silicon film 4 b and the metal film 4 a) of the memory cell region 1A is patterned by etching (preferably dry etching) to form the control gate electrode CG including the metal film 4 a and the silicon film 4 b over the metal film 4 a (Step S7 in FIG. 6). The patterning process in Step S7 may be performed as follows.

A photoresist pattern is formed over the stacked film 4 (although not shown here, the photoresist pattern is formed in a region where the control gate electrode CG is to be formed in the memory cell region 1A and in the whole peripheral circuit region 1B) by using a photolithographic process. Then, by using the photoresist pattern as an etching mask, the stacked film 4 (the stacked film 4 of the silicon film 4 b and the metal film 4 a) is etched (dry-etched) to be patterned. After that, the photoresist pattern is removed.

As described above, the stacked film 4 (the stacked film 4 of the silicon film 4 b and the metal film 4 a) is patterned in Step S7. As shown in FIG. 12, the control gate electrode CG including the patterned stacked film 4 (the stacked film 4 of the silicon film 4 b and the metal film 4 a) is formed in the memory cell region 1A. At this time, in the peripheral circuit region 1B, no patterning of the stacked film 4 (the stacked film 4 of the silicon film 4 b and the metal film 4 a) is performed because the photoresist pattern has been formed as described above. Consequently, the stacked film 4 remains in the whole peripheral circuit region 1B.

In the memory cell region 1A, the insulating film 3 in a part not covered with the control gate electrode CG (sometimes, the interface layer 3 a, too) may be removed by the dry etching performed in the patterning process in Step S7, or by wet etching after the dry etching. The insulating film 3 on the lower part of the control gate electrode CG (when the interface layer 3 a is formed, the interface layer 3 a, too) is not removed by the dry etching in Step S7 and the subsequent wet etching and remains. In the memory cell region 1A, the insulating film 3 (when the interface layer 3 a is formed, the insulating film 3 and the interface layer 3 a) remaining under the control gate electrode CG works as the gate insulating film of the control transistor. Accordingly, the control gate electrode CG including the metal film 4 a and the silicon film 4 b over the metal film 4 a is formed over the semiconductor substrate 1 (the p-type well PW1) via the insulating film 3 (and the interface layer 3 a) being the gate insulating film.

Next, over the side wall of the control gate electrode CG, a side wall insulating film 13 a including an insulator (an insulating film) is formed (Step S8 in FIG. 6). The formation process of the side wall insulating film 13 a in Step S8 can be performed as follows (see FIGS. 13 and 14).

First, as shown in FIG. 13, over the whole main surface of the semiconductor substrate 1, the insulating film 13 is formed (deposited) to cover the control gate electrode CG. The insulating film 13 preferably includes a silicon nitride film. Then, the insulating film 13 is subjected to anisotropic etching (etch back), as shown in FIG. 14, to leave selectively the insulating film 13 over the side wall of the control gate electrode CG. Then, the side wall insulating film 13 a is formed. In this stage, the side wall insulating film 13 a is formed over both side walls of the control gate electrode CG (the side walls 11 a and 11 b) in the memory cell region 1A and over the side wall of the stacked film 4 in the peripheral circuit region 1B.

The formation process of the side wall insulating film 13 a in Step S8 may be omitted. When the side wall insulating film 13 a is formed over the side wall of the control gate electrode CG, the side surface of the metal film 4 a of the control gate electrode CG and the side surface of the insulating film 3 being a high-permittivity film can be covered with the side wall insulating film 13 a. Therefore, it is possible to prevent the metal film 4 a of the control gate electrode CG and the insulating film 3 from being subjected to unnecessary etching in subsequent processes. When the side wall insulating film 13 a is formed, not only the insulating film 5 but also the side wall insulating film 13 a is interposed between the side wall of the control gate electrode CG and that of the memory gate electrode MG which is formed later. Therefore, a breakdown voltage between the control gate electrode CG and the memory gate electrode MG can also be improved.

Next, after performing a washing process to subject the main surface of the semiconductor substrate 1 to a cleaning process, as shown in FIG. 15, over the whole main surface of the semiconductor substrate 1 (over the main surface (the surface) of the semiconductor substrate 1 and over the surface (the upper surface and the side surface) of the control gate electrode CG), the insulating film 5 for the gate insulating film of the memory transistor is formed (Step S9 in FIG. 6). In the peripheral circuit region 1B, because the stacked film 4 remains, the insulating film 5 is formed over the surface (the upper surface and the side surface) of the stacked film 4. Consequently, in Step S9, the insulating film 5 is formed over the semiconductor substrate 1 to cover the control gate electrode CG and the stacked film 4 in the peripheral circuit region 1B. Because the side wall insulating film 13 a is formed over the side walls (11 a and 11 b) of the control gate electrode CG, the side wall insulating film 13 a is interposed between the side walls (11 a and 11 b) of the control gate electrode CG and the insulating film 5.

The insulating film 5 is, as described above, an insulating film having an electric charge accumulation part (an electric charge accumulation layer), and includes, as an insulating film, a stacked film of the silicon oxide film 5 a, the silicon nitride film 5 b and the silicon oxide film 5 c formed in the order from the bottom. To facilitate viewing the drawing, in FIG. 16, the stacked film of the silicon oxide film 5 a, the silicon nitride film 5 b and the silicon oxide film 5 c is illustrated simply as the insulating film 5. Accordingly, actually, as shown in FIG. 16, the insulating film 5 includes the stacked film of the silicon oxide film (an oxide film) 5 a, the silicon nitride film (a nitride film) 5 b over the silicon oxide film 5 a, and the silicon oxide film (an oxide film) 5 c over the silicon nitride film 5 b.

In the insulating film 5, the silicon oxide films 5 a and 5 c can be formed by an oxidation treatment (a thermal oxidation treatment), a CVD process, or a combination of these things. As the oxidation treatment (the thermal oxidation treatment), ISSG (In Situ Steam Generation) oxidation may also be used. In the insulating film 5, the silicon nitride film 5 b can be formed by a CVD process.

In the embodiment, as the insulating film having a trap level (the electric charge accumulation layer), the silicon nitride film 5 b is formed. Although a silicon nitride film is favorable from the viewpoint of reliability, it is not limited to a silicon nitride film. A high-permittivity film having a permittivity higher than that of the silicon nitride film, such as an aluminum oxide film (alumina), a hafnium oxide film, or a tantalum oxide film, can also be used as the electric charge accumulation layer (the electric charge accumulation part). The electric charge accumulation layer (the electric charge accumulation part) can also be formed from silicon nano dots.

To form the insulating film 5, first, over the surface of the semiconductor substrate 1 (the p-type well PW1), over the surface of the control gate electrode CG (over the side surface and the upper surface), and over the surface of the stacked film 4 (over the side surface and the upper surface) the silicon oxide film 5 a is formed by a thermal oxidation process (preferably the ISSG oxidation). As another form, the silicon oxide film 5 a can, also be formed by an ALD process. Then, over the silicon oxide film 5 a, the silicon nitride film 5 b is deposited by a CVD process. Furthermore, over the silicon nitride film 5 b, the silicon oxide film 5 c is formed by a CVD process or thermal oxidation, or by both. Consequently, the insulating film 5 including the stacked film of the silicon oxide film 5 a, the silicon nitride film 5 b and the silicon oxide film 5 c can be formed.

The silicon oxide film 5 a may have a thickness of around from 2 to 10 nm. The silicon nitride film 5 b may have a thickness of around from 5 to 15 nm. The silicon oxide film 5 c may have a thickness of around from 2 to 10 nm.

The insulating film 5 formed in the memory cell region 1A functions as a gate insulating film of the memory gate electrode MG formed later, and has a function of electric charge retention (electric charge accumulation). Because requiring the electric charge retention function, the insulating film 5 has a structure formed by sandwiching an electric charge accumulation layer (the silicon nitride film 5 b) by electric charge blocking layers (the silicon oxide films 5 a and 5 c). The height of potential barrier of the electric charge blocking layer (here, the silicon oxide films 5 a and 5 c) becomes larger than that of potential barrier of the electric charge accumulation layer (the silicon nitride film 5 b).

When the semiconductor device of the modification shown in FIG. 4 is manufactured, as shown in FIG. 17, the insulating film 5 is formed as a stacked film of the silicon oxide film (oxide film) 5 a, the silicon nitride film (nitride film) 5 b over the silicon oxide film 5 a, the silicon oxide film (oxide film) 5 c over the silicon nitride film 5 b, and the insulating film 5 d over the silicon oxide film 5 c. After forming the silicon oxide film 5 a, the silicon nitride film 5 b and the silicon oxide film 5 c as described above, by forming the insulating film 5 d over the silicon oxide film 5 c by a sputtering process, an ALD process, or a CVD process, the insulating film 5 including the stacked film of the silicon oxide film 5 a, the silicon nitride film 5 b, the silicon oxide film 5 c and the insulating film 5 d as shown in FIG. 16 can be formed. The insulating film 5 d may have a thickness of around from 0.5 to 2 nm. Favorable materials as the insulating film 5 d are as described above.

Next, as shown in FIG. 18, over the main surface (the whole main surface) of the semiconductor substrate 1 (over the insulating film 5), the metal film 6 a for forming the memory gate electrode MG is formed (deposited) in the memory cell region 1A to cover the control gate electrode CG and in the peripheral circuit region 1B to cover the stacked film 4 (Step S10 in FIG. 6). Favorable materials as the metal film 6 a are as described above. The metal film 6 a can be formed by a sputtering process. The metal film 6 a may have a thickness (formed film thickness) of around from 10 to 20 nm.

Next, over the main surface (the whole main surface) of the semiconductor substrate 1 (over the metal film 6 a), the silicon film 6 b is formed (deposited) (Step S11 in FIG. 6).

The silicon film 6 b includes a polycrystalline silicon film (a polysilicon film), and can be formed using a CVD process or the like. The silicon film 6 b may have a thickness (a deposited film thickness) of around from 40 to 60 nm. It is also possible to form the silicon film 6 b as an amorphous silicon film in film forming, and form the amorphous silicon film into a polycrystalline silicon film by a subsequent heat treatment.

The silicon film 6 b is more preferably introduced with an impurity (an n-type impurity such as phosphorus (P) or arsenic (As), or a p-type impurity such as boron (B)) to have a low resistivity. The impurity may be introduced into the silicon film 6 b by an ion implantation after the formation of the silicon film 6 b, or may also be introduced into the silicon film 6 b in the formation of the silicon film 6 b. When the impurity is introduced in forming the silicon film 6 b, by including a doping gas (a gas for adding an impurity) in a gas for forming the silicon film 6 b, the silicon film 6 b into which the impurity has been introduced can be formed. The stacked film of the metal film 6 a and the silicon film 6 b over the metal film 6 a is called a stacked film 6.

Next, by an anisotropic etching technology, the stacked film 6 (the stacked film 6 of the silicon film 6 b and the metal film 6 a) is etched back (etching, dry etching, anisotropic etching) to form the memory gate electrode MG (Step S12 in FIG. 6).

In the etch back process of Step S12, by anisotropically etching the stacked film 6 (the stacked film 6 of the metal film 6 a and the silicon film 6 b) (etch back) by the deposited film thickness of the stacked film 6, the stacked film 6 is left over both side walls (side surfaces) 11 a and 11 b of the control gate electrode CG (via the side wall insulating film 13 a and the insulating film 5) in a sidewall spacer shape, and the stacked film 6 in the other regions is removed. Consequently, as shown in FIG. 19, in the memory cell region 1A, the memory gate electrode MG is formed from the stacked film 6 left in a sidewall spacer shape over one side wall 11 a out of both side walls 11 a and 11 b of the control gate electrode CG via the side wall insulating film 13 a and the insulating film 5, and a stacked film spacer SP1 is formed from the stacked film 6 left in a sidewall spacer shape over the other side wall 11 b via the side wall insulating film 13 a and the insulating film 5. The stacked film spacer SP1 may also be considered as a sidewall spacer including the stacked film 6. The memory gate electrode MG is formed over the insulating film 5 to be adjacent to the control gate electrode CG via the side wall insulating film 13 a and the insulating film 5. The memory gate electrode MG and the stacked film spacer SP1 are formed over side walls of the control gate electrode CG opposite to each other, and have approximately symmetric structures while sandwiching the control gate electrode CG. Over the side surface (side wall) of the stacked film 4 left in the peripheral circuit region 1B, too, the stacked film 6 remains in a sidewall spacer shape via the insulating film 5. The stacked film 6 is called a stacked film spacer SP2.

The insulating film 5 is interposed between the memory gate electrode MG, which is formed in Step S12, and the semiconductor substrate 1 (the p-type well PW1), and between the memory gate electrode MG and the control gate electrode CG. The memory gate electrode MG is formed from the metal film 6 a in contact with the insulating film 5 and the silicon film 6 b which is separated from the insulating film 5 via the metal film 6 a. When the side wall insulating film 13 a is formed over the side wall of the control gate electrode CG as described above, the side wall insulating film 13 a and the insulating film 5 result in interposing between the memory gate electrode MG and the control gate electrode CG.

In the stage of performing the etch back process in Step S12, the insulating film 5 in regions not being covered with the memory gate electrode MG and the stacked film spacers SP1 and SP2 is exposed. The insulating film 5 under the memory gate electrode MG in the memory cell region 1A works as the gate insulating film of the memory transistor. By adjusting the deposited thickness of the metal film 6 a and the silicon film 6 b deposited in Steps S10 and S11, the memory gate length can be adjusted.

Next, using a photolithographic technology, a photoresist pattern to cover the memory gate electrode MG and expose the stacked film spacers SP1 and SP2 (not shown) is formed over the semiconductor substrate 1, and then, by dry etching using the photoresist pattern as an etching mask, the stacked film spacers SP1 and SP2 are removed (Step S13 in FIG. 7). After that, the photoresist pattern is removed. By the etching process in Step S13, as shown in FIG. 20, the stacked film spacers SP1 and SP2 are removed, but the memory gate electrode MG is not etched and left because it is covered with the photoresist pattern.

Next, as shown in FIG. 21, in the insulating film 5, parts not covered with the memory gate electrode MG but exposed are removed by etching (by wet etching) (Step S14 in FIG. 7). In the memory cell region 1A, the insulating film 5 located under the memory gate electrode MG and between the memory gate electrode MG and the control gate electrode CG is not removed but is left, and the insulating film 5 in other regions is removed. Also shown in FIG. 21, in the memory cell region 1A, the insulating film 5 extends continuously over both regions of the region between the memory gate electrode MG and the semiconductor substrate 1 (the p-type well PW1) and the region between the memory gate electrode MG and the control gate electrode CG.

When the insulating film 5 is removed in Step S14, the side wall insulating film 13 a over the side wall 11 b of the control gate electrode CG is also removed. FIG. 21 shows the case. As another form, when performing the removal (etching) process of the insulating film 5 in Step S14 so that the side wall insulating film 13 a over the side wall 11 b of the control gate electrode CG is not removed but is left, in the stage in FIG. 21, a state where the side wall insulating film 13 a is formed (remains) over the side wall 11 b of the control gate electrode CG is kept.

Next, by patterning the stacked film 4 in the peripheral circuit region 1B using a photolithographic technology and an etching technology, the gate electrode GE is formed in the peripheral circuit region 1B (Step S14 in FIG. 7). The patterning process in Step S14 can be performed as follows.

Over the main surface of the semiconductor substrate 1, a photoresist pattern is formed using a photolithographic process (although not shown here, the photoresist pattern is formed in a region where the gate electrode GE is formed in the peripheral circuit region 1B and in the whole memory cell region 1A). Then, by using the photoresist pattern as an etching mask, the stacked film 4 (the stacked film 4 of the silicon film 4 b and the metal film 4 a) in the peripheral circuit region 1B is etched (dry-etched) and patterned. Because the memory cell region 1A is covered with the photoresist pattern, the memory gate electrode MG and the control gate electrode CG are not etched. After that, the photoresist pattern is removed.

As described above, as shown in FIG. 22, the gate electrode GE including the patterned stacked film 4 (the stacked film 4 of the metal film 4 a and the silicon film 4 b over the metal film 4 a) is formed in the peripheral circuit region 1B. The gate electrode GE is a gate electrode of a MISFET constituting the peripheral circuit.

Next, over the side walls of the control gate electrode CG and the memory gate electrode MG (the side walls opposite to the sides adjacent to each other via the insulating film 5) and over the side wall of the gate electrode GE, a side wall insulating film 14 including an insulator (an insulating film) is formed (Step S16 in FIG. 7). The process of forming the side wall insulating film 14 in Step S16 can be performed as follows (see FIGS. 23 and 24).

First, as shown in FIG. 23, over the whole main surface of the semiconductor substrate 1, an insulating film 14 d for the side wall insulating film 14 is formed (deposited) to cover the control gate electrode CG, the memory gate electrode MG, and the gate electrode GE. The insulating film 14 d preferably includes a silicon nitride film. Then, by anisotropically etching (etching back) the insulating film 14 d, as shown in FIG. 24, the insulating film 14 d is left selectively over the side walls of the control gate electrode CG and the memory gate electrode MG (the side walls opposite to the side walls adjacent to each other via the insulating film 5) and over the side wall of the gate electrode GE and then the side wall insulating film 14 is formed. The side wall insulating film 14 includes the insulating film 14 d remaining over the side walls of the control gate electrode CG and the memory gate electrode MG (the side walls opposite to the side walls adjacent to each other via the insulating film 5) and over the side wall of the gate electrode GE.

The side wall insulating film 14 is formed over the side wall 11 b of the control gate electrode CG, over the side wall 12 b of the memory gate electrode MG, and over both side walls of the gate electrode GE. The side wall insulating film 14 formed over the side wall 12 b of the memory gate electrode MG is given a symbol 14 a and called the side wall insulating film 14 a. The side wall insulating film 14 formed over the side wall 11 b of the control gate electrode CG is given a symbol 14 b and called the side wall insulating film 14 b. The side wall insulating film 14 formed over both side walls of the gate electrode GE is given a symbol 14 c and called the side wall insulating film 14 c. The side wall 11 b of the control gate electrode CG is the side wall (the side surface) on the side opposite to the side adjacent to the memory gate electrode MG via the insulating film 5 (and the side wall insulating film 13 a) out of the side walls (the side surfaces) of the control gate electrode CG. The side wall 12 b of the memory gate electrode MG is the side wall (the side surface) on the side opposite to the side adjacent to the control gate electrode CG via the insulating film 5 (and the side wall insulating film 13 a) out of the side walls (the side surfaces) of the memory gate electrode MG.

In the case where the side wall insulating film 13 a over the side wall 11 b of the control gate electrode CG is also removed in removing the insulating film 5 in Step S14, when the side wall insulating film 14 is formed in Step S16, the side wall insulating film 14 b formed over the side wall 11 b of the control gate electrode CG includes the side wall insulating film 14 (the remaining part of the insulating film 14 d). FIG. 24 shows the case. As another form, in the case where the side wall insulating film 13 a over the side wall 11 b of the control gate electrode CG is not removed but is left in removing the insulating film 5 in Step S14, when the side wall insulating film 14 is formed in Step S16, the side wall insulating film 14 b formed over the side wall 11 b of the control gate electrode CG includes the stacked film (the stacked structure) of the side wall insulating film 13 a and the side wall insulating film 14 (the remaining part of the insulating film 14 d).

Next, with an ion implantation process, by introducing (doping) an n-type impurity such as arsenic (As) or phosphorus (P) into the semiconductor substrate 1 (the p-type wells PW1 and PW2) using the control gate electrode CG, the memory gate electrode MG and the gate electrode GE as a mask (an ion implantation obstructing mask), as shown in FIG. 25, n⁻-type semiconductor regions (impurity diffused layers) 7 a, 7 b and 7 c are formed (Step S17 in FIG. 7).

On this occasion, the n⁻-type semiconductor region 7 a is formed by self-alignment technique for the side surface of the side wall insulating film 14 a over the side wall 12 b of the memory gate electrode MG in the memory cell region 1A. The n⁻-type semiconductor region 7 b is formed by self-alignment technique for the side surface of the side wall insulating film 14 b over the side wall 11 b of the control gate electrode CG in the memory cell region 1A. The n⁻-type semiconductor region 7 c is formed by self-alignment technique for the side surface of the side wall insulating film 14 c formed over both side walls of the gate electrode GE in the peripheral circuit region 1B. The n⁻-type semiconductor regions 7 a and 7 b can function as a part of a source/drain region (a source region or a drain region) of a memory cell formed in the memory cell region 1A. The n⁻-type semiconductor region 7 c can function as a part of a source/drain region (a source region or a drain region) of a MISFET formed in the peripheral circuit region 1B. The n⁻-type semiconductor regions 7 a, 7 b, and 7 c can be formed by the same ion implantation process, but may also be formed by different ion implantation processes. In the ion implantation for forming the n⁻-type semiconductor regions 7 a, 7 b and 7 c, ions are preferably implanted in a direction perpendicular to the main surface of the semiconductor substrate 1, instead of oblique ion implantation.

Next, ion implantation of a p-type impurity (halo ion implantation) is performed for the semiconductor substrate 1 (the p-type well PW1) in the memory cell region 1A to form a halo region (a p-type semiconductor region) HA (Step S18 in FIG. 7). The halo region HA is formed to encompass (cover) the n⁻-type semiconductor region 7 b, and has an impurity concentration (a p-type impurity concentration) higher than that of the p-type well PW1.

The halo region HA is a halo region formed for the n⁻-type semiconductor region 7 b, and is formed to encompass (cover) the n⁻-type semiconductor region 7 b in the p-type well PW1, and has a conductivity type inverse to that of the n⁻-type semiconductor region 7 b and same as that of the p-type well PW1, and has the p-type (is a p-type semiconductor region). The halo region HA is formed for suppressing the short-channel characteristics (punch through).

In the ion implantation for forming the halo region HA, the control gate electrode CG can function as a mask (an ion implantation-obstructing mask), and the ion implantation for forming the halo region HA is more preferably set to be oblique ion implantation (inclined ion implantation), which enables the halo region HA to be formed precisely to encompass (cover) the n⁻-type semiconductor region 7 b. In general ion implantation, impurity ions are accelerated and driven in a direction perpendicular to the main surface of the semiconductor substrate 1. In oblique ion implantation, impurity ions are accelerated and driven in a direction inclined in a prescribed angle (an angle of inclination) from the direction perpendicular to the main surface of the semiconductor substrate 1.

The n⁻-type semiconductor region 7 b and the halo region HA may be formed not necessarily in this order, but the ion implantation for forming the n⁻-type semiconductor region 7 b and the ion implantation for forming the halo region HA should be performed, at least, after the formation of the control gate electrode CG and before the formation of the sidewall spacer SW described later.

The halo region HA is formed for suppressing short-channel characteristics, and is formed for the n⁻-type semiconductor region 7 b for drain (formed to encompass the n⁻-type semiconductor region 7 b), but the formation of the halo region HA is not necessary for the n⁻-type semiconductor region 7 a for source. Therefore, in the ion implantation for forming the halo region HA, it is only required to cover the n⁻-type semiconductor region 7 a for source with a photoresist pattern so that no p-type halo region is formed for the n⁻-type semiconductor region 7 a. In FIG. 25, ion implantation for forming the halo region HA is performed in such a state that the whole peripheral circuit region 1B and the n⁻-type semiconductor region 7 a in the memory cell region 1A are covered with a photoresist pattern (not shown) to form the halo region HA for the n⁻-type semiconductor region 7 b, but that no halo region is formed for the n⁻-type semiconductor regions 7 a and 7 c. As another form, the halo region may also be formed for the n⁻-type semiconductor regions 7 a and 7 c for suppressing short-channel characteristics.

Next, as shown in FIG. 26, over the whole main surface of the semiconductor substrate 1, an insulating film 15 for the sidewall spacer SW is formed (deposited) (Step S19 in FIG. 7). The insulating film 15 is a single film of a silicon oxide film, or a stacked film of a silicon oxide film and an insulating film over the silicon oxide film. Specifically, the insulating film 15 can be made to be a single film of a silicon oxide film, a stacked film of a silicon oxide film and a silicon nitride film over the silicon oxide film, or a stacked film of a silicon oxide film, a silicon nitride film over the silicon oxide film, and a silicon oxide film over the silicon nitride film.

In forming the insulating film 15 in Step S19, the exposed part of the metal film 6 a having constituted the memory gate electrode MG is oxidized. To be capable of oxidizing the exposed part of the metal film 6 a having constituted the memory gate electrode MG, the formation process of the insulating film 15 is performed. The insulating film 15 is a single film of a silicon oxide film, or a stacked film having a silicon oxide film as the lowermost layer, and, in forming the silicon oxide film, the exposed part of the metal film 6 a is oxidized. For this reason, it is preferable to form, when the insulating film 15 is a single film of a silicon oxide film, the silicon oxide film constituting the single film, and to form, when the insulating film 15 is a stacked film, the lowermost silicon oxide film of the stacked film, under conditions capable of oxidizing the exposed part of the metal film 6 a. Because having strong oxidizing properties, an O₃-TEOS oxide film is a favorable film for oxidizing the exposed part of the metal film 6 a in forming it. The O₃-TEOS oxide film is a silicon oxide film by a thermal CVD process using O₃ (ozone) and TEOS (Tetraethoxysilane, or also called Tetra Ethyl Ortho Silicate) as source gasses. Accordingly, when the insulating film 15 is a single film of a silicon oxide film, preferably the single film is the O₃-TEOS oxide film, and, when the insulating film 15 is a stacked film, preferably the lowermost layer of the stacked film is the O₃-TEOS oxide film.

In the stage directly before the formation of the insulating film 15, the upper end part 16 a of the metal film 6 a is exposed. Accordingly, when the insulating film 15 is formed in Step S19, the upper end part 16 a of the metal film 6 a having constituted the memory gate electrode MG is oxidized to form the metal oxide portion 17 having insulation properties. Because the metal oxide portion 17 is formed by the oxidation of a part of the metal film 6 a, a metal element constituting the metal oxide portion 17 and a metal element constituting the metal film 6 a are the same. When the metal film 6 a is an aluminum (Al) film, the metal oxide portion 17 includes aluminum oxide. Because the side wall insulating film 14 a is formed over the side wall 12 b of the memory gate electrode MG, the side end part 16 b of the metal film 6 a constituting the memory gate electrode MG is covered with the side wall insulating film 14 a but is not exposed. Consequently, when the insulating film 15 is formed in Step S19, the side end part 16 b of the metal film 6 a constituting the memory gate electrode MG is not oxidized. The metal film 6 a is not oxidized. In the upper surface of the memory gate electrode MG, the metal film 6 a is oxidized to form the metal oxide portion 17. In the side surface (side wall 12 b) of the memory gate electrode MG, the metal film 6 a is not oxidized.

When a part of the metal film 6 a is oxidized in the formation of the insulating film 15 to form the metal oxide portion 17, the exposed part of the silicon film 6 b may be slightly oxidized. The material of the metal film 6 a and formation conditions of the insulating film 15 are selected so that the metal film 6 a is oxidized more easily than the silicon film 6 b.

Next, by anisotropically etching (etching back) the insulating film 15, as shown in FIG. 27, when the insulating film 15 is left selectively over the side walls of the control gate electrode CG and the memory gate electrode MG (the side walls on the sides opposite to the sides adjacent to each other via the insulating film 5) and over the side wall of the gate electrode GE, the sidewall spacer SW is formed (Step S20 in FIG. 7). The sidewall spacer SW includes the insulating film 15 remaining over the side walls of the control gate electrode CG and the memory gate electrode MG (the side walls on the sides opposite to the sides adjacent to each other via the insulating film 5) and over the side wall of the gate electrode GE. The sidewall spacer SW1 out of the sidewall spacers SW is formed over the side wall 12 b of the memory gate electrode MG via the side wall insulating film 14 a, and the sidewall spacer SW2 out of the sidewall spacer SW is formed over the side wall 11 b of the control gate electrode CG via the side wall insulating film 14 b.

Next, as shown in FIG. 28, n⁺-type semiconductor regions (impurity diffused layers) 8 a, 8 b and 8 c are formed using an ion implantation process (Step S21 in FIG. 7).

In Step S21, by introducing (doping) an n-type impurity such as arsenic (As) or phosphorus (P) into the semiconductor substrate 1 (the p-type wells PW1 and PW2) using the control gate electrode CG, the memory gate electrode MG and the gate electrode GE, and the sidewall spacer SW (and the side wall insulating films 13 a, 14 a, 14 b and 14 c) over the side walls of these three electrodes as a mask (an ion implantation-obstructing mask), the n⁺-type semiconductor regions 8 a, 8 b and 8 c can be formed. The n⁺-type semiconductor region 8 a is formed by self-alignment technique for the sidewall spacer SW1 over the side wall of the memory gate electrode MG in the memory cell region 1A. The n⁺-type semiconductor region 8 b is formed by self-alignment technique for the sidewall spacer SW2 over the side wall of the control gate electrode CG in the memory cell region 1A. The n⁺-type semiconductor region 8 c is formed by self-alignment technique for the sidewall spacer SW over both side walls of the gate electrode GE in the peripheral circuit region 1B. Consequently, an LDD (lightly doped drain) structure is formed. The n⁺-type semiconductor regions 8 a, 8 b, and 8 c can be formed by the same ion implantation process, but may be formed by different ion implantation processes.

As described above, from the n⁻-type semiconductor region 7 a and the n⁺-type semiconductor region 8 a having a higher impurity concentration than the region 7 a, the n-type semiconductor region MS functioning as the source region of the memory transistor is formed. From the n⁻-type semiconductor region 7 b and the n⁺-type semiconductor region 8 b having a higher impurity concentration than the region 7 b, the n-type semiconductor region MD functioning as the drain region of the control transistor is formed. From the n⁻-type semiconductor region 7 c and the n⁺-type semiconductor region 8 c having a higher impurity concentration than the region 7 c, the n-type semiconductor region functioning as the source/drain region of the MISFET in the peripheral circuit region 1B is formed.

Next, activation annealing being a heat treatment for activating impurities introduced into the n-type semiconductor regions (the n⁻-type semiconductor regions 7 a, 7 b and 7 c and the n⁺-type semiconductor regions 8 a, 8 b and 8 c) for the source and drain is performed (Step S22 in FIG. 7).

As described above, the memory cell MC of the nonvolatile memory is formed in the memory cell region 1A, and the MISFET is formed in the peripheral circuit region 1B.

Next, over the whole main surface of the semiconductor substrate 1, a silicon oxide film is formed by a CVD process or the like. Then, the silicon oxide film (the silicon oxide film is left over silicon regions in which the metal silicide layer 21 should not be formed) is removed using a photolithographic process and an etching process to expose silicon surfaces (silicon regions, silicon films) of the upper surface (surface) of the n⁺-type semiconductor regions 8 a, 8 b and 8 c, the upper surface of the control gate electrode CG, the upper surface of the memory gate electrode MG, and the upper surface of the gate electrode GE. Then, as shown in FIG. 29, over the whole main surface of the semiconductor substrate 1 including over the upper surface (the surface) of the n⁺-type semiconductor regions 8 a, 8 b and 8 c, over the upper surface of the memory gate electrode MG (portions not covered with the sidewall spacer SW), over the upper surface of the control gate electrode CG and over the upper surface of the gate electrode GE, a metal film 20 is formed (deposited) to cover the control gate electrode CG, the memory gate electrode MG, the gate electrode GE, and the sidewall spacer SW. The metal film 20 includes a cobalt (Co) film, a nickel (Ni) film, and a nickel-platinum alloy film, and can be formed using a sputtering process.

Next, by subjecting the semiconductor substrate 1 to a heat treatment, upper layer portions (outer layer portions) of the n⁺-type semiconductor regions 8 a, 8 b and 8 c, the silicon film 4 b of the control gate electrode CG, the silicon film 6 b of the memory gate electrode MG and the silicon film 4 b of the gate electrode GE are caused to react with the metal film 20. Consequently, as shown in FIG. 30, in respective upper parts (upper surfaces, surfaces, upper layer parts) of the n⁺-type semiconductor regions 8 a, 8 b and 8 c, the silicon film 4 b of the control gate electrode CG, the silicon film 6 b of the memory gate electrode MG and the silicon film 4 b of the gate electrode GE, the metal silicide layer 21 is formed. The metal silicide layer 21 may be a cobalt silicide layer (when the metal film 20 is a cobalt film), a nickel silicide layer (when the metal film 20 is a nickel film), or a platinum-added nickel silicide layer (when the metal film 20 is a nickel-platinum alloy film). After that, an unreacted metal film 20 is removed. FIG. 30 shows a cross-sectional view in this stage. As described above, by performing a Salicide (Self Aligned Silicide) process, it is possible to form the metal silicide layer 21 in the upper parts of the n⁺-type semiconductor regions 8 a, 8 b and 8 c, the control gate electrode CG, the memory gate electrode MG and the gate electrode GE, and then to lower the resistances of the source, drain and gate electrodes (CG, MG, GE).

Next, as shown in FIG. 32, over the whole main surface of the semiconductor substrate 1, the interlayer insulating film 22 is formed (deposited) as an insulating film to cover the control gate electrode CG, the memory gate electrode MG, the gate electrode GE, and the sidewall spacer SW. The interlayer insulating film 22 includes a single film of a silicon oxide film, a stacked film of a silicon nitride film and a silicon oxide film formed over the silicon nitride film, thicker than the silicon nitride film, and is formed using a CVD process or the like. After the formation of the interlayer insulating film 22, if necessary, the upper surface of the interlayer insulating film 22 is planarized using a CMP (Chemical Mechanical Polishing) process or the like.

Next, by dry-etching the interlayer insulating film 22 using a photoresist pattern (not shown) having been formed over the interlayer insulating film 22 using a photolithographic process as an etching mask, as shown in FIG. 32, a contact hole (an opening part, through hole) CNT is formed in the interlayer insulating film 22.

Next, in the contact hole CNT, an electroconductive plug PG containing tungsten (W) is formed as a conductor part (a conductor part for connection).

To form the plug PG, over the interlayer insulating film 22 including the inside of the contact hole CNT (over the bottom part and the side wall), a barrier conductor film (a titanium film, a titanium nitride film, or a stacked film of these films) is formed. Then, by forming a main conductor film including a tungsten film over the barrier conductor film to be embedded in the contact hole CNT, and by removing an unnecessary main conductor film and barrier conductor film over the interlayer insulating film 22 by a CMP process, an etch back process or the like, the plug PG can be formed. To simplify the drawing, FIG. 32 shows the barrier conductor film and the main conductor film (the tungsten film) constituting the plug PG integrally.

The contact hole CNT and the plug PG embedded in the contact hole CNT are formed in the upper part of the n⁺-type semiconductor regions 8 a, 8 b and 8 c, the control gate electrode CG, the memory gate electrode MG, and the gate electrode GE. In the bottom part of the contact hole CNT, a part of the main surface of the semiconductor substrate 1, such as a part of the n⁺-type semiconductor regions 8 a, 8 b and 8 c (the metal silicide layer 21 over the surface of the n⁺-type semiconductor regions 8 a, 8 b and 8 c), that of the control gate electrode CG (the metal silicide layer 21 over the surface of the control gate electrode CG), that of the memory gate electrode MG (the metal silicide layer 21 over the surface of the memory gate electrode MG), or that of the gate electrode GE (the metal silicide layer 21 over the surface of the gate electrode GE) are exposed. FIG. 32 shows a cross section in which a part of the n⁺-type semiconductor regions 8 b and 8 c (the metal silicide layer 21 over the surface of the n⁺-type semiconductor regions 8 b and 8 c) is exposed in the bottom part of the contact hole CNT and is connected electrically with the plug PG embedded in the contact hole CNT.

Next, over the interlayer insulating film 22 in which the plug PG is embedded, a wiring (a wiring layer) M1 being a wiring of the first layer is formed. And a case where the wiring M1 is formed using a damascene technology (a single damascene technology) is explained.

First, as shown in FIG. 33, over the interlayer insulating film 22 in which the plug PG has been embedded, the insulating film 24 is formed. The insulating film 24 may also be formed from a stacked film of a plurality of insulating films. Then, after a wiring trench is formed in a prescribed region of the insulating film 24 by dry etching using a photoresist pattern (not shown) as an etching mask, over the insulating film 24 including over the bottom part and the side wall of the wiring trench, a barrier conductor film (a titanium nitride film, a tantalum film, a tantalum nitride, or the like) is formed. Then, over the barrier conductor film, a copper seed layer is formed by a CVD process, a sputtering process, or the like, and, furthermore, over the seed layer, a copper plated film is formed using an electrolytic plating process or the like to embed the copper plated film in the inside of the wiring trench. Then, the main conductor film (the copper plated film and the seed layer) and the barrier conductor film in regions other than the wiring trench are removed by a CMP process to form a wiring M1 of the first layer including the copper embedded in the wiring trench as a main conductive material. To simplify the drawing, FIG. 33 shows the wiring M1 with the barrier conductor film, the seed layer, and the copper plated film integrated.

The wiring M1 is connected electrically with the source region of the memory transistor (the semiconductor region MS), the drain region of the control transistor (the semiconductor region MD), the source/drain region of the MISFET in the peripheral circuit region 113 (the n⁺-type semiconductor region 8 c), the control gate electrode CG, the memory gate electrode MG, the gate electrode GE or the like via the plug PG. After that, wirings of the second layer and subsequent layers are formed by a dual damascene process or the like, but the illustration and explanation are omitted. The wiring M1 and wirings of layers upper than the wiring M1 are not limited to damascene wirings, but may be formed by patterning a conductor film for wiring. The wiring may be a tungsten wiring, an aluminum wiring, or the like.

As described above, the semiconductor device of the embodiment is manufactured.

Next, main characteristics and effects of the embodiment are explained in more detail.

As shown in FIGS. 1, 2 and 4, one of the main characteristics of the semiconductor device of the embodiment is that the memory gate electrode MG has the metal film 6 a adjacent to the insulating film 5, and a silicon film 6 b formed over the metal film 6 a, separated from the insulating film 5 via the metal film 6 a. Specifically, the memory gate electrode MG is formed from a stacked film of the metal film 6 a and the silicon film 6 b over the metal film 6 a, the memory gate electrode MG of the portion contacting with the insulating film 5 is constituted by the metal film 6 a, and the silicon film 6 b of the memory gate electrode MG does not contact with the insulating film 5 and is separated from the insulating film 5 via the metal film 6 a. Another main characteristics of the semiconductor device of the embodiment is that the metal oxide portion 17 is formed in the upper end part of the metal film 6 a.

If the whole memory gate electrode is formed from polysilicon, differing from the embodiment, there is such an anxiety as the generation of the influence of depletion of the memory gate electrode. Consequently, by applying a metal gate electrode to the memory gate electrode, in accordance with the embodiment, it is possible to solve the problem of the depletion of the memory gate electrode, and to improve the performance (electric performance) of the semiconductor device. Because the memory gate electrode and the control gate electrode lie close to each other via a thin insulating film (an insulating film corresponding to the insulating film 5), to improve the reliability even when a metal gate electrode is applied to the memory gate electrode, it is desirable to make the structure which is not liable to short-circuit between the memory gate electrode and the control gate electrode.

In the embodiment, when a metal gate electrode is applied to the memory gate electrode, the memory gate electrode MG is formed from the stacked film of the metal film 6 a and the silicon film 6 b over the metal film 6 a, and the metal oxide portion 17 is formed in the upper end part of the metal film 6 a. The metal oxide portion 17 is formed by the oxidation of a part of the metal film 6 a. If the metal oxide portion 17 is not formed in the upper end part of the metal film 6 a, differing from the embodiment, since there is such an anxiety that the upper end part of the metal film 6 a may short-circuit with the upper end part of the control gate electrode CG because the upper end part of the metal film 6 a lies close to the upper end part of the control gate electrode CG (the end part of the metal silicide layer 21 b in the upper part of the control gate electrode CG). When the metal oxide portion 17 is formed in the upper end part of the metal film 6 a in accordance with the embodiment, the upper end part of the metal film 6 a (16 a) does not lie close to the upper end part of the control gate electrode CG (the end part of the metal silicide layer 21 b in the upper part of the control gate electrode CG) and the insulating metal oxide portion 17 lies between the upper end part of the metal film 6 a (16 a) and the upper end part of the control gate electrode CG. Therefore, the short circuit between the upper end part of the metal film 6 a and that of the control gate electrode CG is prevented.

Moreover, since the silicon film 6 b constituting the memory gate electrode MG is formed over the metal film 6 a being adjacent to the insulating film 5 and separated from the insulating film 5 via the metal film 6 a, the silicon film 6 b constituting the memory gate electrode MG and the metal silicide layer 21 a over the silicon film 6 b are not liable to be short-circuited with the control gate electrode CG. Out of the memory gate electrode MG, the portion that may be most liable to short-circuit with the control gate electrode CG is the upper end part of the metal film 6 a. In the embodiment, the upper end part of the metal film 6 a is oxidized and changed into the insulating metal oxide portion 17 and then the short circuit between the memory gate electrode and the control gate electrode is prevented. Consequently, the reliability of the semiconductor device can be improved.

It may also be considered, differing from the embodiment, to form the whole memory gate electrode from a metal film (not to use the silicon film 6 b). Consequently, the whole upper surface of the memory gate electrode is oxidized to form a metal oxide portion, which takes it difficult to connect the plug PG to the memory gate electrode.

In contrast, in the embodiment, the memory gate electrode MG is set to be a stacked structure of the metal film 6 a being adjacent to the insulating film 5, and the silicon film 6 b formed over the metal film 6 a and separated from the insulating film 5 via the metal film 6 a, and the metal oxide portion 17 formed by oxidizing a part of the metal film 6 a is not formed in the upper part of the silicon film 6 b constituting the memory gate electrode MG. Consequently, when the plug PG is connected to the memory gate electrode MG, it is possible to form the contact hole CNT and the plug PG over the silicon film 6 b and to connect the plug PG to the metal silicide layer 21 a over the silicon film 6 b. Accordingly, the formation of the metal oxide portion 17 never hinders the connection of the plug PG to the memory gate electrode MG.

Further, in the embodiment, when forming the insulating film 15 for the sidewall spacer SW is formed in Step S19, the metal oxide portion 17 having been formed by oxidizing a part of the metal film 6 a is formed, the increase in the number of the manufacturing processes which results from the formation of the metal oxide portion 17 can be regulated.

Moreover, when the metal silicide layer is formed in the upper part of the control gate electrode, a short circuit is liable to occur between the memory gate electrode and the control gate electrode. Therefore, an extremely large effect is obtained by the application of the embodiment and embodiments 2 and 4 below to a case where the metal silicide layer 21 b is formed in the upper part of the control gate electrode CG.

Moreover, when the insulating film 5 includes the insulating film 5 d in the uppermost layer as shown in FIG. 4, the following effects can also be obtained.

In the embodiment, the insulating film 5 includes the insulating film 5 d in the uppermost layer and contacts the insulating film 5 d, and the memory gate electrode MG is formed. The insulating film 5 d is an insulating film that may generate Fermi level pinning. Consequently, because the Fermi level pinning occurs at the interface of the insulating film 5 d and the memory gate electrode MG, the Fermi level can be fixed at a low level (at a low energy position) as compared with the case where the insulating film 5 d does not exist (the case in FIG. 1). Consequently, an action that makes the potential difference (its absolute value) between the memory gate electrode MG and the semiconductor substrate 1 (the p-type well PW1) small can be obtained. By the action, in the case in FIG. 4, it is possible to regulate such a phenomenon that holes accumulated (retained) in the silicon nitride film 5 b go out unnecessarily toward the semiconductor substrate 1 (the p-type well PW1) side, and such a phenomenon that electrons are injected unnecessarily into the silicon nitride film 5 b from the semiconductor substrate 1 (the p-type well PW1) side. As a result, it is possible to improve retention properties of the nonvolatile memory for data (retention properties of the nonvolatile memory for stored information) and to improve the performance (the electric performance) of semiconductor devices having the nonvolatile memory. Moreover, by heightening the permittivity of the insulating film 5 d, even when the insulating film 5 d is added, it is possible to suppress the increase in the effective film thickness (the equivalent oxide film thickness) of the insulating film 5 interposed between the memory gate electrode MG and the semiconductor substrate 1 (the p-type well PW1), as compared with the case where no insulating film 5 d is formed (corresponding to FIG. 1). Consequently, even when the insulating film 5 d is added, since it is possible to regulate or prevent the lowering of electric field generating in the insulating film 5 interposed between the memory gate electrode MG and the semiconductor substrate 1 (the p-type well PW1) in a write operation or in an erase operation, the lowering of the write speed or the erase speed can be prevented.

Accordingly, the insulating film 5 d must be selected from both viewpoints of the capability of generating the Fermi level pinning and having high-permittivity. From the viewpoints, the insulating film 5 d is formed from a metal compound containing at least one of Hf (hafnium), Zr (zirconium), Al (aluminum), Ta (tantalum), and La (lanthanum). Specifically, the particularly favorable material films as the insulating film 5 d include a hafnium oxide film, a zirconium oxide film, an aluminum oxide film, a tantalum oxide film, and a lanthanum oxide film.

Furthermore another main characteristics of the semiconductor device in the embodiment is that a metal gate electrode is applied to the control gate electrode CG. The control gate electrode CG has the metal film 4 a formed over the gate insulating film (the insulating film 3). When a polysilicon gate electrode is applied to the control gate electrode, there is such an anxiety that the control gate electrode is depleted and the driving force lowers. In accordance with the embodiment, by applying a metal gate electrode to the control gate electrode CG, the problem of the depletion of the control gate electrode CG can be solved and the driving force can be improved. Consequently, the performance (the electric performance) of the semiconductor device can be improved.

To improve the performance (the electric performance) of the nonvolatile memory, speeding up the control transistor is important. By applying a metal gate electrode to the control gate electrode CG, the resistance of the control gate electrode CG can be lowered to raise the driving force, too, and the control transistor can be speeded up. Consequently, the performance (the electric performance) of the semiconductor device having the nonvolatile memory can be improved.

When the metal gate electrode is used, as compared with a case where a polysilicon gate electrode is used, the absolute value of the threshold voltage of a MISFET becomes large. The threshold voltage depends also on the impurity concentration in the channel region. When the threshold voltages of the MISFETs is set to be equal in the cases where the metal gate electrode is used and where the polysilicon gate electrode is used, the case where the metal gate electrode is used can lower the impurity concentration in the channel region more than the case where the polysilicon gate electrode is used.

When threshold voltages are set to be equal in the case where the metal gate electrode is used for the control gate electrode CG and in the case where the polysilicon gate electrode is used for it, the impurity concentration in the control transistor channel region can be lowered in the case where the metal gate electrode is used for the control gate electrode CG more than in the case where the polysilicon gate electrode is used for it. The channel region of the control transistor means a channel region formed on the lower side of the control gate electrode CG, and, specifically, corresponds to the channel region formed on the lower side of the insulating film 3 in the lower part of the control gate electrode CG in the p-type well PW1 (the semiconductor substrate 1). In the embodiment, it is possible to lower the impurity concentration in the channel region of the control transistor by applying the metal gate electrode to the control gate electrode CG, as compared with the case where the polysilicon gate electrode is applied to the control gate electrode.

In the embodiment, the impurity concentration in the channel region of the control transistor is, more preferably, set to be not more than 1×10¹⁷/cm³. The reason why the channel region of the control transistor has such low impurity concentration is as follows.

To make a nonvolatile memory have a higher capacity and a smaller size, it is effective to make the cell size of the nonvolatile memory smaller. The gate length of the control gate electrode is desired to be made smaller. When the gate length of the control gate electrode is made small, to compensate accompanying lowering of the threshold voltage, the impurity concentration in the channel region of the control transistor needs to be increased. If the impurity concentration in the channel region of the control transistor is increased when the gate length of the control gate electrode is made small, a leak current 31 shown in FIG. 34 may increase. FIG. 34 is an explanatory view for explaining the leak current 31, and shows the same cross-sectional view as FIG. 1. In FIG. 34, the region 32 surrounded by a doted line corresponds to a substrate region (a Si substrate region) in which an inversion layer (the inversion layer behaves as an n-type region) is formed, when holes are accumulated in the insulating film 5, by the holes accumulated in the insulating film 5, and the inversion layer (the region 32) is formed just beneath the insulating film 5 under the memory gate electrode MG.

When holes are accumulated in the insulating film 5 to form the inversion layer in the region 32, a leak current flows through a path shown by an arrow to which a symbol 31 is given in FIG. 34 (the leak current is called a leak current 31). The leak current 31 flows from the n⁺-type semiconductor region 8 a to the semiconductor substrate 1, via the n⁻-type semiconductor region 7 a, the inversion layer (the inversion layer formed in the region 32), the channel region of the control transistor (corresponding to a region 33 surrounded by a dashed one-dotted line in FIG. 34), the halo region HA, and the p-type well PW1. The higher the impurity concentration in the channel region of the control transistor becomes, the easier the leak current 31 flows (the leak current 31 increases). This is because a higher impurity concentration in the channel region of the control transistor (corresponding to the region 33 surrounded by the dashed one-dotted line in FIG. 34) leads to a stronger electric field and makes the leak current 31 flow easier.

As described above, if the impurity concentration in the channel region of the control transistor is increased when the gate length of the control gate electrode CG is made small, the leak current 31 may increase. In the embodiment, because the absolute value of the threshold voltage of the control transistor can be made large by using the metal gate electrode for the control gate electrode CG, even when the gate length of the control gate electrode CG is made small, it is unnecessary to lower the impurity concentration in the channel region of the control transistor. Even when the gate length of the control gate electrode is made small, the accompanying lowering of the threshold voltage can be compensated by applying the metal gate electrode to the control gate electrode CG, instead of increasing the impurity concentration in the channel region of the control transistor. Consequently, in the embodiment, as the result of applying the metal gate electrode to the control gate electrode CG, it becomes possible to lower the impurity concentration in the channel region of the control transistor, the leak current 31 can be regulated to improve the reliability of the semiconductor device having the nonvolatile memory. Moreover, it is also possible to improve the retention properties of data, and to improve the performance (the electric performance) of the semiconductor device having the nonvolatile memory. Also, the variation of characteristics between memory cells of the nonvolatile memory can be regulated or prevented.

When the gate length of the control gate electrode CG is made small, particularly when the gate length of the control gate electrode CG is not more than 80 nm, the leak current 31 is liable to become large, the embodiment and embodiments 3, 4 and 5 below exert large effect when they are applied to cases where the gate length of the control gate electrode CG is not more than 80 nm. And, the leak current 31 can be regulated by lowering the impurity concentration in the channel region of the control transistor, and the effect becomes large when the impurity concentration in the channel region of the control transistor is not more than 1×10¹⁷/cm³. Consequently, in the embodiment and embodiments 3, 4 and 5 below, the impurity concentration in the channel region of the control transistor is more preferably not more than 1×10¹⁷/cm³.

In the embodiment, the metal gate electrode is applied to the control gate electrode CG, as described above, preferably a high-permittivity gate insulating film is applied to the gate insulating film (the insulating film 3) of the control transistor. As the result of the reduction of cell size of nonvolatile memories, that of the thickness of control transistors has proceeded, but there is such an anxiety that, when a thin silicon oxide film is used as a gate insulating film, a tunneling current may occur, in which electrons flowing through the channel of the control transistor tunnel a barrier formed by the gate insulating film of the silicon oxide to flow into the control gate electrode. However, by applying a high-permittivity gate insulating film to the gate insulating film (the insulating film 3) of the control transistor, because a physical film thickness can be increased when the capacity is set to be the same, it is possible to reduce the leak current tunneling the gate insulating film of the control transistor and flowing into the control gate electrode CG. Consequently, the reliability of the semiconductor device having the nonvolatile memory can furthermore be improved.

Further, because the increase in the absolute value of the threshold voltage of the control transistor can be achieved by applying a high-permittivity gate insulating film to the gate insulating film (the insulating film 3) of the control transistor, as described above, it becomes possible to furthermore lower the impurity concentration in the channel region of the control transistor, and to regulate furthermore the leak current 31. Consequently, the reliability of the semiconductor device having the nonvolatile memory can furthermore be improved.

Embodiment 2

FIG. 35 is a cross-sectional view of essential parts of the semiconductor device in the embodiment 2, and corresponds to FIG. 1 in the embodiment 1. The semiconductor device in the embodiment is also a semiconductor device including a nonvolatile memory. FIG. 35 shows a cross-sectional view of essential parts in the memory cell region of the nonvolatile memory.

The semiconductor device in the embodiment differs from that in the embodiment 1 in the control gate electrode CG and the gate insulating film of the control transistor. In the embodiment 1, the control gate electrode CG is formed from the metal film 4 a and the silicon film 4 b over the metal film 4 a. In the embodiment 2, the control gate electrode CG does not have the metal film 4 a but is formed from a single film of the silicon film 4 b. The metal silicide layer 21 b is formed in the upper part of the silicon film 4 b is the same in the embodiments 2 and 1. In the embodiment 1, the control gate electrode CG is a metal gate electrode. In the embodiment 2, the control gate electrode CG is a polysilicon gate electrode (a gate electrode including polysilicon).

Further, in the embodiment 1, the gate insulating film of the control transistor is formed form the insulating film 3 being a high-permittivity film, or from the stacked structure (the stacked film) of the interface layer 3 a and the insulating film 3. In the embodiment 2, the gate insulating film of the control transistor is formed from the insulating film 3 b including a silicon oxide film or a silicon oxynitride film. In the embodiment 2, between the control gate electrode CG including the silicon film 4 b and the semiconductor substrate 1 (the p-type well PW1), the insulating film 3 b including a silicon oxide film or a silicon oxynitride film is formed, and the insulating film 3 b (the insulating film 3 under the control gate electrode CG) functions as the gate insulating film of the control transistor. In the embodiment 2, as the result of applying the polysilicon gate electrode to the control gate electrode CG and applying the insulating film 3 b including a silicon oxide film or a silicon oxynitride film to the gate insulating film of the control transistor, the formation of the side wall insulating film 13 a is omitted.

Because the other structure of the semiconductor device in the embodiment is fundamentally the same as that in embodiment 1, the explanation is omitted.

Next, the process of manufacturing a semiconductor device of the embodiment is explained. Differences from the manufacturing process of the embodiment 1 are mainly explained.

FIGS. 36 and 37 are cross-sectional views of essential parts in the process of manufacturing a semiconductor device in the embodiment. FIGS. 36 and 37 show cross sections corresponding to those of the embodiment 1 in FIGS. 8 to 15 and 18 to 33.

To manufacture the semiconductor device in the embodiment, after performing Steps S1, S2 and S3 in the same manner as in the embodiment 1, as shown in FIG. 36, the surface of the semiconductor substrate 1 (the p-type wells PW1 and PW2) is cleaned by diluted hydrofluoric acid cleaning, and the insulating film 3 b for the gate insulating film is formed over the main surface of the semiconductor substrate 1 (the surfaces of the p-type wells PW1 and PW2). The insulating film 3 b can be formed from a thin silicon oxide film or silicon oxynitride film. The thickness (formed thickness) of the insulating film 3 b may be around 2 to 3 nm. Instead of performing the formation process of the interface layer 3 a and the insulating film 3 in Step S4 in the embodiment 1, the formation process of the insulating film 3 b is performed in the embodiment 2.

Then, in the embodiment, without forming the metal film 4 a, as shown in FIG. 36, the silicon film 4 b for the gate electrode is formed (deposited) over the main surface (the whole main surface) of the semiconductor substrate 1 (over the insulating film 3 b). Instead of forming the stacked film 4 of the metal film 4 a and the silicon film 4 b in Steps S5 and S6 in the embodiment 1, a single film of the silicon film 4 b is formed in the embodiment 2.

Then, the silicon film 4 b in the memory cell region 1A is etched (preferably dry-etched) and patterned to form the control gate electrode CG including the silicon film 4 b. Instead of patterning the stacked film 4 of the metal film 4 a and the silicon film 4 b to form the control gate electrode CG in Step S7 in the embodiment 1, the silicon film 4 b is patterned to form the control gate electrode CG in the embodiment 2.

In the embodiment 2, as the result of applying the polysilicon gate electrode to the control gate electrode CG and applying the insulating film 3 b including a silicon oxide film or a silicon oxynitride film to the gate insulating, film of the control transistor, the formation process of the side wall insulating film 13 a in Step S8 is omitted.

Subsequent processes are fundamentally the same as in the embodiment 1, and the explanation is omitted. In the embodiment 2, regarding the control transistor, structures of the gate insulating film and the control gate electrode CG are different from those in the embodiment 1. In the embodiment 2, the control gate electrode CG is a polysilicon gate electrode, and the gate insulating film of the control transistor is a silicon oxide film or a silicon oxynitride film. The effects resulted from applying a metal gate electrode to the control gate electrode CG and applying a high-permittivity gate insulating film to the gate insulating film of the control transistor in the embodiment 1 can not be obtained. In the embodiment 2, the structure of the memory transistor is the same as that in the embodiment 1. Consequently, effects resulted from the structure of the memory transistor (the structure of the memory gate electrode MG, the formation of the metal oxide portion 17, and the structure of the insulating film 5) in the embodiment 1 can also be obtained in the embodiment 2 (the repeated explanation of the effect is omitted).

Embodiment 3

FIG. 38 is a cross-sectional view of essential parts of the semiconductor device in the embodiment 3, and corresponds to FIG. 1 in the embodiment 1. The semiconductor device in the embodiment is also a semiconductor device including a nonvolatile memory. FIG. 38 shows a cross-sectional view of essential parts of the memory cell region of the nonvolatile memory.

The semiconductor device in the embodiment differs from that in the embodiment 1 in the memory gate electrode MG of the memory transistor. In the embodiment 1, the memory gate electrode MG is formed from the metal film 6 a and the silicon film 6 b over the metal film 6 a. In the embodiment 3, the memory gate electrode MG does not have the metal film 6 a, and is formed from the single film of the silicon film 6 b. As the result that the memory gate electrode MG does not have the metal film 6 a, the metal oxide portion 17 is also not formed. In the embodiment 3, the memory gate electrode MG includes the single film of the silicon film 6 b and the metal silicide layer 21 is formed in the upper part of the silicon film 6 b. In the embodiment 1, the memory gate electrode MG is a metal gate electrode. In the embodiment 3, the memory gate electrode MG is a polysilicon gate electrode (a gate electrode including polysilicon).

Moreover, in the embodiment, as the result that a polysilicon gate electrode is applied to the memory gate electrode MG, the metal oxide portion 17 is not formed, and the formation of the side wall insulating films 14 a and 14 b may also be omitted. FIG. 38 shows a case where the formation of the side wall insulating films 14 a and 14 b are omitted. When an offset spacer is necessary in the ion implantation process for forming the n⁻-type semiconductor regions 7 a and 7 b (corresponding to Step S17), in the same manner as in the embodiment 1, the side wall insulating films 14 a and 14 b may also be formed in the embodiment 3. FIG. 38 shows a case where the side wall insulating film 13 a over the side wall 11 b of the control gate electrode CG has not been removed.

The other structure of the semiconductor device of the embodiment is fundamentally the same as that of the embodiment 1, and the explanation is omitted.

Next, the process of manufacturing a semiconductor device of the embodiment is explained. Differences from the manufacturing process of the embodiment 1 are mainly explained.

FIGS. 39 and 40 are cross-sectional views of essential parts in the process of manufacturing a semiconductor device in the embodiment 3. FIGS. 39 and 40 show cross sections corresponding to those in FIGS. 8 to 15 and 18 to 33 in the embodiment 1.

To manufacture the semiconductor device in the embodiment, first, in the same manner as in the embodiment 1, processes until Step S9 are performed to obtain the structure in FIG. 15. Then, without forming the metal film 6 a, as shown in FIG. 39, over the main surface (the whole main surface) of the semiconductor substrate 1 (over the insulating film 5), the silicon film 6 b for forming the memory gate electrode is formed (deposited), in the memory cell region 1A, to cover the control gate electrode CG, and, in the peripheral circuit region 1B, to cover the stacked film 4. Instead of forming the stacked film 6 of the metal film 6 a and the silicon film 6 b in Steps S10 and S11 in the embodiment 1, a single film of the silicon film 6 b is formed in the embodiment 3.

Then, by etching back (etching, dry-etching, anisotropically etching) the silicon film 6 b by an anisotropic etching technology, the memory gate electrode MG including the silicon film 6 b is formed. Instead of forming the memory gate electrode MG by etching back the stacked film 6 of the metal film 6 a and the silicon film 6 b in Step S12 in the embodiment 1, the silicon film 6 b is etched back to form the memory gate electrode MG in the embodiment 3. In forming the memory gate electrode MG by etching back the silicon film 6 b, the stacked film spacers SP1 and SP2 are also formed. In the embodiment 1, the stacked film spacers SP1 and SP2 are formed from the stacked film 6 of the metal film 6 a and the silicon film 6 b. In the embodiment 3, the stacked film spacers SP1 and SP2 include the silicon film 6 b.

Because subsequent processes are fundamentally the same as in the embodiment 1, the explanation is omitted. But, in the embodiment 3, as the result of applying a polysilicon gate electrode to the memory gate electrode MG, the metal oxide portion 17 is not formed in forming the insulating film 15 in Step S19. The formation process of the side wall insulating film 14 in Step S16 can also be omitted.

In the embodiment 3, regarding the memory transistor, the structure of the memory gate electrode MG is different from that in the embodiment 1. In the embodiment 3, because the memory gate electrode MG is a polysilicon gate electrode, effects obtained as the result of applying a metal gate electrode to the memory gate electrode MG and forming the metal oxide portion 17 in the embodiment 1 cannot be obtained in the embodiment 3. However, in the embodiment 3, the structure of the control transistor is the same as that in the embodiment 1. Consequently, effects resulted from the structure of the control transistor (the structure of the control gate electrode CG, the structure of the gate insulating film of the control transistor) in the embodiment 1 can also be obtained in the embodiment 3 (the repeated explanation is omitted).

Embodiment 4

FIG. 41 is a cross-sectional view of essential parts of the semiconductor device in the embodiment 4, and corresponds to FIG. 1 in the embodiment 1. The semiconductor device in the embodiment is also a semiconductor device including a nonvolatile memory. FIG. 41 shows a cross-sectional view of essential parts of the memory cell region of the nonvolatile memory.

The semiconductor device in the embodiment is different from the semiconductor device in the embodiment 1 in the following point. In the embodiment 1, the metal oxide portion 17 is formed in the upper end part (16 a) of the metal film 6 a constituting the memory gate electrode MG. In the embodiment 4, the metal oxide portion 17 is formed in the upper end part (16 a) of the metal film 6 a constituting the memory gate electrode MG and the metal oxide portion 17 a is formed in the side end part (16 b) of the metal film 6 a. In addition, in the embodiment 4, a metal oxide portion 18 is formed in the end part (particularly in both end parts in the gate length direction of the control gate electrode CG) of the metal film 4 a constituting the control gate electrode CG. Moreover, the side wall insulating films 13 a, 14 a and 14 b formed in the embodiment 1 are not formed in the embodiment 4.

The other structure of the semiconductor device in the embodiment is fundamentally the same as that in the embodiment 1, and the explanation is omitted.

The metal oxide portions 17 a and 18 are explained specifically. Because the metal oxide portion 17 is the same as that in the embodiment 1, the explanation is omitted.

On the side end part 16 b side of the metal film 6 a constituting the memory gate electrode MG, the metal oxide portion 17 a having insulating properties is formed. The metal oxide portion 17 a is formed by the oxidation of a part of the metal film 6 a, and the side end part 16 b of the metal film 6 a is adjacent to (in contact with) the metal oxide portion 17. Adjacent to the side end part 16 b of the metal film 6 a, the metal oxide portion 17 a is formed continuously to the metal film 6 a. Consequently, the side end part of the metal film 6 a is oxidized and the metal oxide portion 17 a is formed in the side end part of the metal film 6 a. Because the sidewall spacer SW1 is formed over the side wall of the memory gate electrode MG, the metal oxide portion 17 a is formed between the side end part 16 b of the metal film 6 a and the sidewall spacer SW1.

Because the metal oxide portion 17 a is formed by the oxidation of a part of the metal film 6 a, the metal element constituting the metal oxide portion 17 a and the metal element constituting the metal film 6 a are the same. Also, the metal element constituting the metal oxide portion 17 a, the metal element constituting the metal oxide portion 17, and the metal element constituting the metal film 6 a are the same. When the metal film 6 a is an aluminum (Al) film, the metal oxide portion 17 and the metal oxide portion 17 a include aluminum oxide.

Because the side end part of the metal film 6 a is oxidized to form the metal oxide portion 17 a, at least a part of the metal oxide portion 17 a lies on the lower side of the silicon film 6 b constituting the memory gate electrode MG. At least a part of the metal oxide portion 17 a lies between the silicon film 6 b constituting the memory gate electrode MG and the insulating film 5. Specifically, because the metal oxide portion 17 a is sandwiched vertically by the silicon film 6 b constituting the memory gate electrode MG and the insulating film 5 and is sandwiched laterally (in the gate length direction) by the metal film 6 a and the sidewall spacer SW1, the metal oxide portion 17 a is surrounded by the silicon film 6 b constituting the memory gate electrode MG, the insulating film 5, the metal film 6 a, and the sidewall spacer SW1.

In the end part of the metal film 4 a constituting the control gate electrode CG (particularly, in both end parts in the gate length direction of the control gate electrode CG), the metal oxide portion 18 having insulating properties is formed. The metal oxide portion 18 is formed by the oxidation of a part of the metal film 4 a, and the end part of the metal film 4 a (particularly, both end parts in the gate length direction of the control gate electrode CG) is adjacent to (contacts with) the metal oxide portion 18. Consequently, the end part of the metal film 4 a constituting the control gate electrode CG (particularly, both end parts in the gate length direction of the control gate electrode CG) is oxidized, and the metal oxide portion 18 is formed in the end part of the metal film 4 a constituting the control gate electrode CG (particularly, in both end parts in the gate length direction of the control gate electrode CG).

Because the metal oxide portion 18 is formed by the oxidation of apart of the metal film 4 a, the metal element constituting the metal oxide portion 18 and the metal element constituting the metal film 4 a are the same. When the metal film 4 a is an aluminum (Al) film, the metal oxide portion 18 includes aluminum oxide. Because the metal oxide portion 18 is formed by the oxidation of the end part of the metal film 4 a constituting the control gate electrode CG, at least a part of the metal oxide portion 18 lies on the lower side of the silicon film 4 b constituting the control gate electrode CG. At least a part of the metal oxide portion 18 lies between the silicon film 4 b constituting the control gate electrode CG and the insulating film 3. Specifically, because the metal oxide portion 18 is sandwiched vertically by the silicon film 4 b constituting the control gate electrode CG and the insulating film 3 and is sandwiched laterally (in the gate length direction) by the metal film 4 a constituting the control gate electrode CG, and the sidewall spacer SW2 or the insulating film 5, the metal oxide portion 18 is surrounded by the silicon film 4 b constituting the control gate electrode CG, the insulating film 5, the metal film 4 a, and the sidewall spacer SW2 or the insulating film 5.

Next, the process of manufacturing a semiconductor device of the embodiment 4 is explained. Differences from the manufacturing process of the embodiment 1 are mainly explained.

FIGS. 42 to 52 are cross-sectional views of essential parts in the process of manufacturing a semiconductor device in the embodiment 4. FIGS. 42, 44, 46, 47, 49, and 51 show cross sections corresponding to those of the embodiment 1 in FIGS. 8 to 15 and 18 to 33. FIG. 43 is a partially enlarged cross-sectional view of FIG. 42. FIG. 45 is a partially enlarged cross-sectional view of FIG. 44. FIG. 48 is a partially enlarged cross-sectional view of FIG. 47. FIG. 50 is a partially enlarged cross-sectional view of FIG. 49. FIG. 52 is a partially enlarged cross-sectional view of FIG. 51.

To manufacture the semiconductor device in the embodiment 4, processes until Step S7 are performed in the same manner as in the embodiment 1 to obtain the structure in FIGS. 42 and 43 that is the same as that in FIG. 12. Then, in the embodiment 4, without performing the formation process of the side wall insulating film 13 a in Step S8, the formation process of the insulating film 5 in Step S9 is performed to obtain the structure in FIGS. 44 and 45. FIG. 45 shows the case where the insulating film 5 is formed as the stacked film of the silicon oxide film 5 a, the silicon nitride film 5 b over the silicon oxide film 5 a, and the silicon oxide film 5 c over the silicon nitride film 5 b. As a modification, the insulating film 5 can be formed as the stacked film of the silicon oxide film 5 a, the silicon nitride film 5 b over the silicon oxide film 5 a, the silicon oxide film 5 c over the silicon nitride film 5 b, and the insulating film 5 d over the silicon oxide film 5 c.

In the embodiment, as shown in FIGS. 44 and 45, informing the insulating film 5, the side wall insulating film 13 a is not formed over the side wall of the control gate electrode CG, and the insulating film 5 is formed over the main surface (the surface) of the semiconductor substrate 1 and over the surface (the upper surface and the side surface) of the control gate electrode CG. In the peripheral circuit region 1B, the insulating film 5 is formed over the surface (the upper surface and the side surface) of the stacked film 4. A large difference from the embodiment 1 is that, in forming the silicon oxide film 5 a being the lowermost layer of the insulating film 5, the end part of the metal film 4 a having constituted the control gate electrode CG (particularly, both end parts in the gate length direction of the control gate electrode CG) is oxidized to form the metal oxide portion 18 having insulating properties. In the embodiment 4, in a stage immediately prior to forming the insulating film 5, the side wall insulating film 13 a is not formed over the side wall of the control gate electrode CG, and the end part of the metal film 4 a constituting the control gate electrode CG (particularly, both end parts in the gate length direction of the control gate electrode CG) is exposed. Consequently, in forming the silicon oxide film 5 a being the lowermost layer of the insulating film 5, it is possible to oxidize the end part of the metal film 4 a having constituted the control gate electrode CG (particularly, both end parts in the gate length direction of the control gate electrode CG) to form the metal oxide portion 18. In the peripheral circuit region 1B, too, in places where the end part of the metal film 4 a is exposed, the metal oxide portion 18 is formed in the same manner. The metal oxide portion 18 formed in the peripheral circuit region 1B is removed in the process of forming the gate electrode GE in later Step S15.

Moreover, in forming the silicon oxide film 5 a, the end part of the metal film 4 a of the control gate electrode CG (particularly, both end parts in the gate length direction of the control gate electrode CG) is oxidized to form the metal oxide portion 18. The silicon oxide film 5 a is preferably formed under such conditions that can oxidize the exposed part of the metal film 4 a. Because ISSG (In Situ Steam Generation) oxidation has strong oxidizing properties, the formation of the silicon oxide film 5 a by the ISSG oxidation is favorable to oxidize the exposed part of the metal film 4 a in the formation of the silicon oxide film 5 a. Consequently, in the embodiment 4, the silicon oxide film 5 a is preferably formed by the ISSG oxidation.

When a part of the metal film 4 a is oxidized in forming the silicon oxide film 5 a to form the metal oxide portion 18, the exposed part of the silicon film 4 b may slightly be oxidized. The material of the metal film 4 a and the condition for forming the silicon oxide film 5 a are selected so that the metal film 4 a is more easily oxidized than the silicon film 4 b.

After the insulating film 5 is formed, processes until forming the gate electrode GE in Step S15 are fundamentally the same as those in the embodiment 1. Steps S10, S11, S12, S13, S14, and S15 are performed in the same manner as in embodiment 1 to obtain the structure in FIG. 46 corresponding to FIG. 22. Then, in the embodiment 4, without performing the formation process of the side wall insulating film 14 in Step S16, Step S17 (the process of forming the n⁻-type semiconductor regions 7 a, 7 b and 7 c) and Step S18 (the process of forming the halo region HA) are performed to obtain the structure in FIG. 47 corresponding to FIG. 25. FIG. 48 is a partially enlarged cross-sectional view of FIG. 47. In the embodiment 4, Step S17 (the process of forming the n⁻-type semiconductor regions 7 a, 7 b and 7 c) and Step S18 (the process of forming the halo region HA) are performed when no side wall insulating film 14 is formed over the side walls of the control gate electrode CG, the memory gate electrode MG, and the gate electrode GE. The other points are fundamentally the same as Steps S17 and S18 in the embodiment 1.

In the embodiment 4, the process of forming the insulating film 15 in Step S19 is performed to obtain a structure in FIG. 49 corresponding to FIG. 26. FIG. 50 is a partially enlarged cross-sectional view of FIG. 49.

In the embodiment, too, when the insulating film 15 is formed in Step S19, the exposed part of the metal film 6 a having constituted the memory gate electrode MG is oxidized. Specifically, as described above, the insulating film 15 is a single film of a silicon oxide film or a stacked film in which the lowermost layer is a silicon oxide film. When the silicon oxide film is formed, the exposed part of the metal film 6 a constituting the memory gate electrode MG is oxidized. In the embodiment 4, what are different from the embodiment 1 are that the side wall insulating film 14 (14 a) is not formed over the side wall of the memory gate electrode MG in the stage immediately prior to forming the insulating film 15 and that not only the upper end part of the metal film 6 a constituting the memory gate electrode MG but also the side end part (16 b) of the metal film 6 a is exposed. Consequently, when the insulating film 15 is formed in Step S19, in the embodiment 4, too, in the same manner as in the embodiment 1, the upper end part 16 a of the metal film 6 a having constituted the memory gate electrode MG is oxidized to form the metal oxide portion 17 having insulating properties, and, differing from the embodiment 1, the side end part 16 b of the metal film 6 a having constituted the memory gate electrode MG is oxidized to form the metal oxide portion 17 a having insulating properties. Because the metal oxide portion 17 and the metal oxide portion 17 a are formed by the oxidation of parts of the metal film 6 a, the metal elements constituting the metal oxide portions 17 and 17 a and the metal element constituting the metal film 6 a are the same.

Because the formation process of the side wall insulating film 14 in Step S16 is not performed, no side wall insulating film 14 (14 c) is formed over the side wall of the gate electrode GE, and, in a stage immediately prior to forming the insulating film 15, the end part (the side surface) of the metal film 4 a constituting the gate electrode GE is also exposed. Consequently, in the embodiment 4, when the insulating film 15 is formed in Step S19, not only the exposed parts of the metal film 6 a (the upper end part and side end part) having constituted the memory gate electrode MG are oxidized to form the metal oxide portions 17 and 17 a, but also the end part (the side surface) of the metal film 4 a having constituted the gate electrode GE is oxidized to form a metal oxide portion 19 having insulating properties is formed. The metal oxide portion 19 is formed in the end part of the metal film 4 a having constituted the gate electrode GE (particularly, in both end parts in the gate length direction of the gate electrode GE), and the metal element constituting the metal oxide portion 19 and the metal element constituting the metal film 4 a are the same.

When a part of the metal films 4 a and 6 a is oxidized in the formation of the insulating film 15 to form the metal oxide portions 17, 17 a and 19, a case where exposed parts of the silicon films 4 b and 6 b are slightly oxidized may occur. The materials of the metal films 4 a and 6 a and formation conditions of the insulating film 15 are selected so that the metal films 4 a and 6 a are oxidized more easily than the silicon films 4 b and 6 b.

The subsequent processes are fundamentally the same as in embodiment 1. In the embodiment 4, too, an anisotropic etching (etching back) process of the insulating film 15 in Step S20 is performed in the same manner as in embodiment 1 to form the sidewall spacer SW and then to obtain the structure in FIG. 51 corresponding to FIG. 27. FIG. 52 is partially enlarged cross-sectional view of FIG. 51. After that, in the same manner as in the embodiment 1, the process in Step S21 (the formation process of the n⁺-type semiconductor regions 8 a, 8 b and 8 c) and subsequent processes are performed. The repeated explanation is omitted.

In the embodiment, in addition to the effect of the embodiment 1, the following effects can be obtained.

Because the metal oxide portion 18 is formed in the end part of the metal film 4 a constituting the control gate electrode CG (particularly, both end parts in the gate length direction of the control gate electrode CG), an effective gate length L_(eff) of the control gate electrode CG can be shortened by the portion of the metal oxide portion 18. Because the ON current can be increased, the driving force can be improved. Accordingly, the performance (electric performance) of the semiconductor device having the nonvolatile memory can furthermore be improved.

Moreover, since the metal oxide portion 17 a is formed in the side end part (16 b) of the metal film 6 a constituting the memory gate electrode MG, even when no offset spacer like that in the side wall insulating film 14 a exists, the end part (the starting point) of a region into which an impurity is implanted in the ion implantation process for forming the n⁻-type semiconductor region 7 a can be separated from the side end part 16 b of the metal film 6 a constituting the memory gate electrode MG by the portion of the metal oxide portion 17 a. Consequently, it is possible to reduce the leak current and to improve the short-channel characteristics. In addition, because the offset spacer like that in the side wall insulating film 14 a becomes unnecessary, the reduction of cell size of the memory cell (the cell size in the gate length direction) becomes possible, and the size (the area) of the semiconductor device can be reduced.

In the embodiment 2, it is also possible to form the metal oxide portions 17 and 17 a for the metal film 6 a of the memory gate electrode MG. In the embodiment 3, it is also possible to form the metal oxide portion 18 for the metal film 4 a of the control gate electrode CG.

Embodiment 5

In the embodiment 5, the control gate electrode CG of the nonvolatile memory in the embodiment 3 is formed from a stacked film of the metal film 4 a, the silicon film 4 b, and the insulating film.

FIG. 53 is a cross-sectional view of essential parts of the semiconductor device in the embodiment 5, and corresponds to FIG. 1 in the embodiment 1 and FIG. 38 in the embodiment 3. The semiconductor device in the embodiment is also a semiconductor device including a nonvolatile memory. FIG. 53 shows a cross-sectional view of essential parts of the memory cell region of the nonvolatile memory.

As shown in FIG. 53, in the memory cell of the nonvolatile memory in the embodiment, the control gate electrode CG is constituted by a stacked film (a stacked pattern, stacked structure) of the metal film 4 a, the silicon film 4 b and the insulating film 41. More specifically, the control gate electrode CG is constituted by the stacked film (the stacked film pattern) of the metal film 4 a, the silicon film 4 b over the metal film 4 a, the insulating film 41 a over the silicon film 4 b, and the insulating film 41 b over the insulating film 41 a. The insulating film 41 is constituted by the insulating film 41 a over the silicon film 4 b and the insulating film 41 b over the insulating film 41 a, and the insulating film 41 a is thinner than the insulating film 41 b. The insulating film 41 a includes preferably a silicon oxide film, and the insulating film 41 b includes preferably a silicon nitride film.

In the embodiment, because the insulating film 41 (insulating films 41 a and 41 b) is formed in the upper part of the control gate electrode CG of the memory cell, no metal silicide layer 21 is formed over the control gate electrode CG of the memory cell. What is obtained by replacing the control gate electrode CG formed from the metal film 4 a, the silicon film 4 b over the metal film 4 a, and the metal silicide layer 21 (21 b) over the silicon film 4 b in the embodiment 3 by the control gate electrode CG formed from the stacked film of the metal film 4 a, the silicon film 4 b over the metal film 4 a, and the insulating film 41 over the silicon film 4 b corresponds to the semiconductor device in the embodiment 5.

Because the other structure of the memory cell of the embodiment is the same as that in the embodiment 3, the explanation is omitted.

Next, the process of manufacturing a semiconductor device of the embodiment is explained. Differences from the manufacturing process in the embodiment 3 are mainly explained.

FIGS. 54 and 55 are cross-sectional views of essential parts in the process of manufacturing a semiconductor device in the embodiment 5. FIGS. 54 and 55 show cross sections corresponding to those in FIGS. 8 to 15 and 18 to 33 in the embodiment 1.

In the embodiment, between Step S6 (the formation process of the silicon film 4 b) and Step S7, as shown in FIG. 54, a process of forming the insulating film 41 over the silicon film 4 b is added. The process of forming the insulating film 41 has a process of forming the insulating film 41 a over the silicon film 4 b, and a process of forming the insulating film 41 b over the insulating film 41 a.

In Step S7, in the embodiment 3, the stacked film 4 of the metal film 4 a and the silicon film 4 b over the metal film 4 a are patterned to form the control gate electrode CG. In the embodiment 5, the stacked film of the metal film 4 a, the silicon film 4 b over the metal film 4 a, and the insulating film 41 over the silicon film 4 b is patterned. Consequently, as shown in FIG. 55, the control gate electrode CG including the stacked film pattern of the metal film 4 a, the silicon film 4 b over the metal film 4 a, and the insulating film 41 over the silicon film 4 b is formed. Between Step S7 and Step S8, in regions where the insulating film 41 is to be removed (such as the peripheral circuit region 1B), the insulating film 41 is removed. Since subsequent processes (Step S8 and following Steps) are fundamentally the same as those in the embodiment 3, the explanation is omitted.

In the embodiment 5, too, the same effects as those in the embodiment 3 can be obtained.

Moreover, in the embodiment, because the control gate electrode CG is formed from the stacked film of the metal film 4 a, the silicon film 4 b and the insulating film 41 (more specifically the insulating films 41 a and 41 b), even when the metal film 4 a and the silicon film 4 b are formed thinner than those in the embodiment 3, the height of the memory gate electrode MG formed in a sidewall spacer shape over the side wall of the control gate electrode CG can be kept.

Furthermore, in the embodiment, following effects can also be obtained. When the insulating film 41 is formed in the upper part of the control gate electrode CG, the metal silicide layer 21 can not be formed in the upper part of the control gate electrode CG. Therefore, when the control gate electrode is a polysilicon gate electrode, differing from the embodiment, the resistance of the control gate electrode becomes high, which is disadvantageous for the speeding up of the control transistor. In contrast, in the embodiment 5, the control gate electrode CG has the metal film 4 a and is a metal gate electrode. Although the metal silicide layer 21 is not formed in the upper part of the control gate electrode CG as the result of forming the insulating film 41 in the upper part of the control gate electrode CG, the resistance of the control gate electrode CG can be reduced. Consequently, it is possible to speed up the control transistor and to improve the performance (the electric performance) of the semiconductor device having the nonvolatile memory.

FIG. 56 is a cross-sectional view of essential parts of a semiconductor device of a modification in the embodiment 5, and corresponds to FIG. 53 and FIG. 1 in the embodiment 1.

The modification in FIG. 56 is obtained by setting the control gate electrode CG to have the structure same as that of the control gate electrode CG in FIG. 53 (the stacked structure of the metal film 4 a, the silicon film 4 b, and the insulating film 41), in the memory cell in FIG. 1 in the embodiment 1. Specifically, in the modification in FIG. 56, in the same manner as in the memory cell in FIG. 53, the control gate electrode CG is constituted by the stacked film (the stacked film pattern) of the metal film 4 a, the silicon film 4 b over the metal film 4 a, the insulating film 41 a over the silicon film 4 b, and the insulating film 41 b over the insulating film 41 a. Over the control gate electrode CG, no metal silicide layer 21 is formed. Because the other structure of the memory cell of the modification in FIG. 56 is the same as that of the embodiment 1, the explanation is omitted.

The modification in FIG. 56 can also be considered as a case where, in the memory cell in FIG. 53, the memory gate electrode MG is a metal gate electrode (a stacked structure of the metal film 6 a and the silicon film 6 b) and the metal oxide portion 17 is formed.

In the modification in FIG. 56, in the same manner as the memory cell in FIG. 53, no metal silicide film 21 b is formed over the control gate electrode CG. In the process shown in FIG. 28 (Step S21), when the potential difference between the control gate electrode CG and the memory gate electrode MG becomes large as the result of implantation of an impurity (ion implantation) into a portion exposed in the upper portions of the side wall insulating film 13 a and the insulating film 5, there is such an anxiety that a leak current may flow in the upper part of the control gate electrode CG and the memory gate electrode MG. As shown in FIG. 56, by forming the metal oxide portion 17, the metal oxide portion 17 having insulating properties lies between the upper part of the control gate electrode CG and the upper part of the memory gate electrode. The distance between electroconductive films in the upper part of the control gate electrode CG and the upper part of the memory gate electrode MG becomes long. Accordingly, the generation of the leak current can be prevented or decreased.

Furthermore, as modifications in the embodiment 5, the metal oxide portion 18 may be formed in the memory cell in FIG. 53 and in the memory cell in FIG. 56, the metal oxide portion 17 a may be formed in the memory cell in FIG. 56, and the metal oxide portions 17 a and 18 may be formed in the memory cell in FIG. 56.

The invention achieved by the inventors is explained on the basis of the embodiments. The invention is not limited to the embodiments and can be changed in a range that does not deviate from the purport.

The invention is effective when applied to semiconductor devices and technologies of manufacturing the devices. 

1. A semiconductor device, comprising: a semiconductor substrate; first gate electrode formed in an upper part of the semiconductor substrate; a second gate electrode that is formed in an upper part of the semiconductor substrate and is adjacent to the first gate electrode; a first insulating film formed between the first gate electrode and the semiconductor substrate; and a second insulating film that is formed between the second gate electrode and the semiconductor substrate and between the first gate electrode and the second gate electrode, and that includes an electric charge accumulation part, wherein: the second gate electrode has a first metal film adjacent to the second insulating film and a first silicon film that is formed over the first metal film and is separated from the second insulating film via the first metal film; and a first metal oxide portion is formed in an upper end part of the first metal film.
 2. The semiconductor device according to claim 1, wherein a metal element constituting the first metal oxide portion and a metal element constituting the first metal film are the same.
 3. The semiconductor device according to claim 2, wherein the first metal oxide portion is formed by oxidation of a part of the first metal film.
 4. The semiconductor device according to claim 3, wherein a first metal silicide layer is formed in an upper part of the first silicon film.
 5. The semiconductor device according to claim 4, wherein a second metal silicide layer is formed in an upper part of the first gate electrode.
 6. The semiconductor device according to claim 5, wherein: the semiconductor device has a nonvolatile memory; and the first and second gate electrodes are gate electrodes constituting the nonvolatile memory.
 7. The semiconductor device according to claim 6, wherein: a sidewall spacer is formed over a side wall that is a side wall of the second gate electrode and that is on a side opposite to the side adjacent to the first gate electrode; and a second metal oxide portion is formed between an end part located on an opposite side of the upper end part of the first metal film and the sidewall spacer.
 8. The semiconductor device according to claim 7, wherein at least apart of the second metal oxide portion is located between the first silicon film and the second insulating film.
 9. The semiconductor device according to claim 8, wherein the second metal oxide portion is formed by oxidation of a part of the first metal film.
 10. The semiconductor device according to claim 9, wherein the first gate electrode has a second metal film formed over the first insulating film, and a second silicon film formed over the second metal film, and the second metal silicide layer is formed in an upper part of the second silicon film.
 11. The semiconductor device according to claim 10, wherein the first insulating film is a high-permittivity film.
 12. The semiconductor device according to claim 11, wherein impurity concentration in a channel region below the first gate electrode in the semiconductor substrate is not more than 1×10¹⁷/cm³.
 13. A semiconductor device, comprising: a semiconductor substrate; a first gate electrode formed in an upper part of the semiconductor substrate; a second gate electrode that is formed in an upper part of the semiconductor substrate and is adjacent to the first gate electrode; a first insulating film formed between the first gate electrode and the semiconductor substrate; a second insulating film that is formed between the second gate electrode and the semiconductor substrate and between the first gate electrode and the second gate electrode, and that includes an electric charge accumulation part, wherein the first gate electrode has a metal film formed over the first insulating film.
 14. The semiconductor device according to claim 13, wherein the first gate electrode further has a silicon film formed over the metal film.
 15. The semiconductor device according to claim 14, wherein the first insulating film is a high-permittivity film.
 16. The semiconductor device according to claim 15, wherein impurity concentration in a channel region below the first gate electrode in the semiconductor substrate is not more than 1×10¹⁷/cm³.
 17. The semiconductor device according to claim 16, wherein: the semiconductor device has a nonvolatile memory; and the first and second gate electrodes are gate electrodes constituting the nonvolatile memory.
 18. The semiconductor device according to claim 17, wherein an end part of the metal film in a gate length direction of the first gate electrode is oxidized.
 19. A method of manufacturing a semiconductor device having: a semiconductor substrate; a first gate electrode and a second gate electrode that are formed in an upper part of the semiconductor substrate and are adjacent to each other; a first gate insulating film formed between the first gate electrode and the semiconductor substrate; and a second gate insulating film that is formed between the second gate electrode and the semiconductor substrate and that has an electric charge accumulation part therein, the method comprising the steps of: (a) providing the semiconductor substrate; (b) forming a first insulating film for the first gate insulating film on a main surface of the semiconductor substrate; (c) forming a first conductor film for the first gate electrode over the first insulating film; (d) patterning the first conductor film to form the first gate electrode; (e) forming a second insulating film that is for the second gate insulating film and that includes an electric charge accumulation part, on a main surface of the semiconductor substrate and on a surface of the first gate electrode; (f) forming a first metal film over the second insulating film; (g) forming a first silicon film over the first metal film; (h) etching-back a stacked film of the first silicon film and the first metal film to leave the stacked film over a side wall of the first gate electrode via the second insulating film, and to form the second gate electrode; (i) removing the second insulating film in a portion not covered with the second gate electrode to leave the second insulating film between the second gate electrode and the semiconductor substrate, and between the first gate electrode and the second gate electrode; and (j) oxidizing an upper end part of the first metal film exposed from an upper surface of the second gate electrode to form a first metal oxide portion.
 20. The method of manufacturing a semiconductor device according to claim 19, further comprising the steps of: (k) forming a third insulating film to cover the first and second gate electrodes over the semiconductor substrate; and (l) etching-back the third insulating film to leave the third insulating film over side walls of the first and second gate electrodes on sides opposite to sides adjacent to each other, and to form a sidewall spacer, wherein: the third insulating film formed in the step (k) includes a single film of a first silicon oxide film, or a stacked film having the first silicon oxide film as the lowermost layer; and in the step (j), an upper end part of the first metal film is oxidized in forming the first silicon oxide film to form the first metal oxide portion.
 21. The method of manufacturing a semiconductor device according to claim 20, wherein, in the step (j), a end part that is located on a side opposite to the upper end part of the first metal film and that is exposed from a side wall on a side opposite to a side adjacent to the first gate electrode of the second gate electrode is oxidized to form a second metal oxide portion.
 22. The method of manufacturing a semiconductor device according to claim 21, further comprising the step of, after the step (l), (m) forming a metal silicide layer in an upper part of the first silicon film constituting the second gate electrode and in that of the first gate electrode.
 23. The method of manufacturing a semiconductor device according to claim 19, further comprising the steps of, after the step (i) and before the step (j): (i1) forming a silicon nitride film to cover the first and second gate electrodes over the semiconductor substrate; and (i2) etching-back the silicon nitride film to leave the silicon nitride film over side walls of the first and second gate electrodes on sides opposite to sides adjacent to each other, and to expose an upper end part of the first metal film from an upper surface of the second gate electrode. 